Furnace blower comes on by itself/won't shut off

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Out of nowhere, my furnace blower came on (without heat). I just moved into this house and have not even turned on the heater once! I could not turn it off by fiddeling with the thermostat, so I crawled under the house and found an off-switch. Also turned off the pilot light. Called a serviceman and, after looking at it for two minutes, he recommended a brandnew furnace ($ 3,500.00 gasp!) or a repair for $ 500.00 (not recommended). I would like a second opinion, perhaps there is something I can do myself??? Thanks, Anne

-- Annemarie Engelhardt (annemarie.engelhardt@kp.org), June 17, 2002


Annemarie, Last year we had almost the same thing happen to our new furnace. One day in July the house kept getting hotter & hotter. I went to the garage & found our furnace on although the thermostat was turned off. Since it was still under warranty I called the installer and in our case there was something wrong in the thermostat. The thermostat was replaced ($30.00) and we've had no problems since. Now I know you said your furnace isn't on just the blower but I think the thermostat is still responsible for turning the blower on & off. Before replacing or even having it repaired I'd call another repair place preferably one that specializes working on the brand of furnace you have. If that doesn't seem possible, try calling the manufacturer directly, many times they have a service department or repair hotline to answer customer questions. Maybe they even have an owners guide if you don't have one that would give you the troubleshooting list & possible fixes. Good Luck, KA

-- Kathy Aldridge (beckoningwinds@yahoo.com), June 18, 2002.

Annemarie! The problem is cause by a mechanical fan switch. It turns the blower on when a certain tempature is achieved inside the furnace. Usually about 110F turns it on. In summertime it doesnt' take much extra heat [sometimes none] to activate it. A pilot light emitts enough heat to kick it on. Solution is to turn off the voltage to the furnace if no central a/c is using the furnace for air circulation. In addition to turnin off the current to the furnace the Pilot llight can also be turned off. Not much heat usually needed in an already hot house! Let me know how it turns out.

Oh, BTW-I was the head serviceman for a major propane company for almost 35 years. I don't know it all but I knon a bunch! old hoot. Matt.24:44

-- old hoot gibson (hoot@pcinetwork.com), June 18, 2002.

that was my guess Hoot,, 3,500 bucks for a 3 dollar switch,, seems like a deal to me

-- Stan (sopal@net-pert.com), June 18, 2002.

I am having just the opposite thing happen... It is cold and so the furnace kicks on and lights a flame but the fan never turns on and blows out air. A service man told us we needed a digital thermostat $80 plus 72 to install. maybe we have nearly the same part messed up?

-- Joe Ellsworth (ellsjoe@yahoo.com), October 21, 2002.

Joe! The serviceman don't know what he's talkin about. The Thermostat does not have anything to do with the fan comin on or not. It's job is soley to control the furnace. When the T-stat calls for heat the funace will light. After the furnace is warm enought [depending upon how the mechanical fanswhitch is set] the blower will come on. The problem is either in the fan switch or the blower motor if this is an older furnace. [Newer, computered ones works off a timer] With a little more info I might be able to help out a mite more. Email me with the type, brand and appx age of the furnace.

Where ya'll located? I'm in S.E. IL. old hoot. Matt.24:44

-- old hoot (hoot@pcinetwork.com), October 22, 2002.

Annemarie, google up "how stuff works". check out gas furnaces ect.. sounds like a bad limit switch, simple thing. be SURE the power is off when YOU replace it. good luck.

-- Zen Clown (MartyS@iland.net), October 22, 2002.

Here's one for you. The blower goes on for several minutes (blowing cool air) before the heat starts pouring in. Everything else works fine. Is this a thermostat issue or something else? Thank you.

-- LOU (louv@ATTBI.COM), December 26, 2002.

Lou! Does the furnace fire first or does the blower come on first? How old is the furnace--is it a computerd one?

If it's the older type without the computer then the blower is controlled by a fan switch which turns it on. Heat has to be in the furnace before the fanswitch can kick on the blower. If it's this type the the ductwork has to be cold and takin a few minutes to warm it up with the warm air from the furnace.

If it's a computered furnace--the blowers sometimes comes on too quickly. . Blower function is controlled by a timer --a relay in the puter board. This is caused by a faulty board usually caused by lighting or a line surge

The other option is---a hybred furnace--a puter board to "fire" the furnace and a mechanical fan switch to kick on the fan. This doesn't sould like your furnace as a mechanical fan switch will not turn the blower on until heat has built up in the furnace. old hoot. Matt.24:44

-- old hoot (hoot@pcinetwork.com), December 26, 2002.

I hope anyone can help me with this problem: The motor in my furnace stared squealing about a week ago, no other noises or problems with the furnace, other than the loud squeal when the fan first started up. The noise lasted for about 30 secs before it stopped. Finally, after a few days the motor seized. I replaced the motor yesterday, but now the fan turns on for about 2 minutes then off for about 2 minutes. It warms fine, the furnace is burning, and there are no noises or squeals, but it just turns off constantly. I was told that it could be the limit switch, and I was thinking maybe the thermostat. The only thing is, I didnít have the problem with it turning on and off before I put in the new motor. Do you have any ideas on what could be going on here? I really don't wanna go on a wild goose chase. I appreciate any help you can give.

-- Jon Roybal (jroybal2002@hotmail.com), December 27, 2002.

Thought I might post an update to my furnace blower problem. I have replaced my thermostat (old Honeywell round one, three wires) with a new digital (the wiring was a challenge!). The furnace ran two heating cycles without problems, but then the darn fan would not shut off, constantly blowing cold air. Another website recommended giving the furnace a slight "whack" to dislodge stuck limit/fan switch. That worked. But I have to do it every time! Can you picture that: having to crawl under the house several times a day to "whack" the limit/fan switch. Is it hard to replace those? I am on the do-it- yourself warpath, ever since these heating contractors tried to pull one on me. Thanks for any advice. Anne

-- Anne (annemarie.engelhardt@kp.org), December 30, 2002.

Happy new Year all... thought I might try to help answer your "Q".... well since you changed the Motor Jon .. The thing I would suspect from what you have detailed .... is the belt is too tight and the Motor is kicking out on over load . could be the limit switch also ..but I doubt it ..... have a look at the limit switch.. should be 3 pins to set limit on\off

1. should be around 200 *C <-- High limit \ shutdown 2. should be around 150* C <-- Fan On 3. should be around 100*C <-- Fan Off

Hope that helps you out somewhat anyway !

Gamble's Heating \ Air Conditioning

-- Bill Stark (bstark@rogers.com), January 04, 2003.


I am experiencing about the same problem with my furnace. When I turn on the furnace, the furnace will not stop blowing out the hot air, and it goes beyond what is set on the thermostat.

Can someone give me any ideas on how to fix this, I replaced the thermostat already. I have a thought that it might be my "heat anticipator" setting, but I work with computers, not heating utilities!! :)


(please reply to this message by email please, or whatever..)

-- Jon B. (machstem@hotmail.com), January 14, 2003.

Hello all,

Jon B...... Yea that sounds right to me also that sympton seems like Heat anticipator .. assuming you have a standard T stat not digital . also Jon is this a high efficient or Mid ? I would say good place to start is peel the top door off the Furnace and usually on the Front left side of furnace will be a Manufactures tag with Btu\h ratings and such ..... pretty sure you will find anticipator settins as well on most ... good luck :-)

-- B.Stark (bstark@rogers.com), January 14, 2003.

Our 4 year-old furnace has a 2-speed blower; the low speed is to circulate the air in the house and the higher speed kicks in to blow warm air to maintain the set temperature. Sounds great in theory but the low speed circulating the air in the house feels like cold air and I hate it. We do not have a switch to turn off the low speed, however, in 2001 the service man told us we could simply disconnect one of the red wires which we did and it was wonderful. We had the furnace cleaned in the fall 2002 and this service man told us that we run the chance of burning out the motor by not having the lower speed running prior to the higher (heat-up) speed coming on. Frankly, I would love to burn out the motor and replace the darn thing with a blower motor with a switch that I can easily turn off rather than suffer the cold air blowing at my feet all the time but it is only 4 years old.

Has anyone disconnected the low speed and if so have you had any problems? Any suggestions.

-- (yfile@sunlife.com), January 15, 2003.

well for that 4 year old Furnace.......I would say it would be a lot cheaper to Run a 18\4 or 18\5 "T" stat wire (only need 3 wires 4 For A\C)RED= Heat \ WHITE= Heat \ GREEN= Fan\YELLOW= A\C (If you got AC Then RED= Heat\Cool) Depending on Stat a Heat\cool stat will have a Fan switch like this FAN-OFF-AUTO on one side and HEAT-OFF-COOL on the other. On most standard heat\cool stats (honeywell)you'll need to jumper the RED-Heat RED-Cool Terminals For A\C Digital Honeywell the jumper is installed..... 2 speed or 3 speed? should be 3 speed FAN=LOW \ HEAT=MEDIUM \ HIGH=COOL sounds like the installer Wired the LOW speed to a constant power. you will need to take the jumper between the LOW speed and the constant power out and find the Continuous ( CONT ) terminal on the board and re-connect it to the lead coming off it..... Good Luck :-)

-- B.Stark (bstark@rogers.com), January 15, 2003.

I have a problem with my furnace. Wondering if anyone is familiar with it. My furnace kicks in and runs for its usual few minutes. Then it shuts off. A few minutes later it kicks in again, but it only runs for anywhere between 3 - 10 seconds and shuts off again. Usually the fan hasn't even got up to full speed before the furnace turns off. It does this routinely. Runs for a few minutes, off, runs for a few seconds, off. I have a programmable Honeywell thermostat. I am going to change the battery in it tonight and see if that makes a difference. The battery indicator is not on, but I'm going to give it a shot. Anyone else have any suggestions?

-- Cheryl Fuchs (cfuchs@qhrsoftware.com), February 25, 2003.


The thermocuple was too far from your pilot light because the pilot light should heat up the thermocuple to activate the flame. If it is too far away from the pilot light it will turn on a few secon and turn off again. Try to push the thermocuple in the path of the pilot light and see.


-- Pony Yim (PonyYim@yahoo.com), March 20, 2003.

Cheryl! I'm assuming you're talking about the funace blower that runs a short time---off a little bit and runs again? I also assume the flame continues to burn during this entire process?

If the flame does burn--your problem is caused by either insufficient flame [could be spider webs in the burners, burner orfices, low gas pressure, faulty fan switch or problems with the return air. Cold air is cooling the fan switch off faster than the furnace can produce heat.

If the flame is off and on ---need to check the amp draw setting on the thermostat. That amp draw located on the side of the gas valve has to match the anticipator setting on the thermostat.

The pilot light has nothing to do with the burn cycle or output of the burners. It's job solely is a safety. When the pilot goes out the t-couple will cool off and the main valve will close---preventing any gas from flowing through the valve.

Hope this helps. old hoot. Matt.24:44

-- old hoot (oldhoot@shawneelink.net), March 21, 2003.

Spider webs. Learned that one the hard way!

-- Zen Clown (martys@iland.net), March 22, 2003.

I have another question...

Our blower doesn't seem to be shutting off. The heater/blower is inactive, until it is triggered by the thermostat (too cold). Then, the heater and blower turn on. Once the temperature in the house is warm enough, the heater turns off, but the blower continues. If the house gets cool enough again (or if I set the desired temp very high), the heater turns on again.

I've read some of the previous questions/answers and can add the following:

I think the furnace is probably kind of old, though it seems to me that the blower comes on before the furnace sometimes (can't verify that-- only know that when it "kicks on" some cold air precedes the heated air).

We live in San Francisco, where it's about 50F right now. I doubt that the blower is being triggered by the furnace interior reaching 110F.

We have lived in this house/had this furnace for a little over 2 years. Until recently, it has worked well. Some nights, however, the furnace doesn't seem to turn on, even though the desired temp is 69F, but the actual temp in the house is 62F. The pilot light goes out more than I would think it should (twice in the past 4 months-- is that too much?). The blower not shutting off just started two days ago. I shut the furnace off manually, left it off for several hours, and restarted it. Yesterday it seemed to work fine. This morning, the blower is staying on, even after the heater is off.

I just went down and looked. There were two little switch type things, and the one that looked to be for the blower had a range of 80-120. It looked like mine was set at a little over 100. I nudged it up just a bit, and the blower shut off. So, it looks to me like maybe that switch is sensing that the internal temp of the furnace is 100F even when it's not? Why would it only recently start doing that?

It's a natural gas furnace.

I like doing things myself, and love to learn how things work in the process. Would like to try to fix this myself. Any suggestions? With the combination of problems, does it sound like we just need a new furnace? Or would a new thermostat and a new blower switch do the trick?

Thanks in advance!! So glad I found this thread!

Kim in San Francisco

-- Kim Lovy (kimklovy@yahoo.com), March 28, 2003.

Kim! I would come all the way out there to fix your furnace but it looks like I'm fix'n to be busy this weekend! LOL!! It appears the blower problems is solely in the fan/limit switch. The setting of 80 to 110 is too low. Pilot lights will make the blowers run if the setting is too low.

The 110f has to be achieved before the blower comes on. When the blower runs -[during heating cycle] it will continue until the t-stat is satisfied. The burners will go off and the blower will continue until the 80f is achieved and then it shuts the blower off. The Lower temp needs to be raise to about 90f and the 110f needs to be moved to 120f.

Just guessing I'd imagine the fan switch is a mechanical one and sometimes after age they will get contacts that are pitted. Don't mess with it while the "juice" is on--it carries 120 volts! It may or may not have a limit switch in the same enclousre. Honeywell as well as White/Rogers both made similar fan/limit switches and both had litle round dials with pointers that were movable on'm. When moving those pointers hold the dial so it won't turn.

The pilot light is dirty more than likely or it wouldn't go out. Check and see if the pilot flame is burning blue or yellow. Yellow means the pilot burner and/or orfice is dirty.

I don't think the t-stat is faulty from what you describe.

Let me know how it turns out! old hoot. Matt.24:44

-- old hoot (oldhoot@shawneelink.net), March 28, 2003.

Not sure if my problem is the same as Cheryl's. The burner and fan cycle normally, then later when the burner has been off for a while the fan comes on and runs for usually just a few seconds. I watched the fan switch and can see the heat build up and trip it at about 110 degrees. After the fan runs for just a few seconds the switch drops suddenly and goes off. (It's a Honeywell and I can see the temp on its dial.) Last season we had a guy come out, he charged us $200 to replace the fan switch but it didn't fix the problem. Fat chance we'll ask him back. Maybe old hoot can suggest something. Furnace is nearly 30 years old. I tried setting the lower limit lower (from about 85 down to 80). Didn't help. Is it safe to try bumping upper limit up, as you suggested to someone else? I'll try 120 if it won't burn the house down.

-- Ray G (rqb@beer.com), March 29, 2003.

Ray! The Honeywell fan switch probably has a limit in it also, I'm guessin. If so there should be 3 pointers on it. The highest one is the limit and should be set higher by abut 20f than the "fan on" temp. I wouldn't change the limit switch setting.

The lower temp you changed from 85 to 80 is the "fan off" setting. I'd put it back to about 85 or 90 while moving the "fan on" from the present settin to about 15f higher than the "fan off".

What you describe with the fan coming back on is a normal thing in older furnaces. As they get older they tend to do it more and more. Nothing wrong and it won't hurt anything. Completely safe and it won't burn your house down.

That feller who charged you $200 surely didn't know what he was doin. A Honeywell or White/Rogers fan/limit switch costs $19. Purty good profit and especially when it didn't fix't. Take care. old hoot. Matt.24:44

-- old hoot (oldhoot@shawneelink.net), March 29, 2003.

Thanks for the response, oldhoot.

When you cautioned me about turning off the power before I muck with the fan switch, you mean turn off the juice before I replace the switch, right, not just before I modify the temp on the fan switch?

This morning I put the off temp on the fan switch at 100F, and it did *finally* shut off-- but long after the burner/heater had shut off. The fan switch doesn't seem to have a different pointer for setting the on temp. There is only one pointer, and that is to the temp off. Also, there is no display to show what the temperature is in there.

If it helps, our furnace is a Midland-Ross, model 20-100 (??). I think that means it's ancient. The limit switch is model 5C02-51. That has only one pointer on it, can be set to a range of 150-250F, and has "Stop setting 200" engraved on the switch. The fan switch is model 5C22-52.

It seems to me I just need to get a new fan switch. Will look into doing that some time soon-- I have toddler twins at home, so I am pretty busy!!

At what age would you recommend a new furnace, even though the other one works perfectly well? Or would you never do that?

Thanks, oldhoot, for your help. It seems we're keeping you pretty busy!

Kim in SanFran

-- Kim Lovy (kimklovy@yahoo.com), March 30, 2003.

Kim! It appears by what you say, that your furnace is an ancient one and the fan switch is really worn out! Some of those old dudes are good'ns but they do take a little more gas to operate. I can't really recommend you changing out the furnace with a new one because I don't know the condition of yours. I would, however, have somebody you can trust to look it over closely and see the condition of the burners, heat exchanger [firebox] blower and vent system. If they are all in fairly good shape I'd just consider replacing the fan switch. I kinda gather by your description that it will me next to impossible to find a replacement fan switch without changing things around a mite. When I encounter an old dude that has obsolete parts like yours I rewire and use a new fan/limit combination switch. I doubt if you will be able to do that but a GOOD furnace man can. Preferrably an old dude like me who'se had to workin on things rather than replace the entire furnace.

When I replace those weird fan switches and separate limits I used the Honeywell with the 8" insertion probe. Removed the old limit, fan switch and use the new one. Much easier to take care of in the future. Like I said on another post they cost me about $19 or so. Lowes or Home Depot should have'm for about that price or so.

Be safe even when movin the pointers---turn off the power! I don't like that "slow walkin--low talkin" events they call funerals!! God Bless. old hoot. Matt.24:44

-- old hoot (oldhoot@shawneelink.net), March 30, 2003.

I have a problem. Recently my furnance has been acting up. It is a Heil SP80 manufactured by Inter-City Products model number NCC5125BKB2. The furnance was installed in 1995 and I put in a Honeywell 3400 programmable thermostat in 1996. It has worked perfect until recently. The furnance is electronic ignition. Here is what has started:

The combustion blower comes on for about 30 seconds and then the flame fires up and then the main blower comes on and heats up the house. When the cycle completes the flame goes out and the main blower continues to blow which is normal. Then the problem begins. Before the main blower shuts off the combustion blower starts again for approximately 5 seconds and then shuts off. It continues to this anywhere from 5 to 20 times before completely shuting down. Sometimes the main blower shuts off and the combustion blower continues to cycle on and off several times. I thought I had a bad thermostat so I put my old mercury stat back on and everything worked great for 2 months. At this point I was very confident that my Honeywell 3400 stat was bad and that I needed to replace it so I bought a new Honeywell programmable stat model 3600 and hooked it up and I had the same problems with this one.

I finally called a service man because I couldn't figure out what was wrong since my mercury stat would work fine and my 2 programmable ones would not. He hooked up a volt meter and tested it and said that "power stealing" thermostats were not compatible with my furnance and that I needed to buy one what was completely hard wired or one that totally ran off batteries and didn't use any power from the furnance.

What I don't understand is if my Honeywell 3400 was not compatible with my Heil SP80 furnance why has it worked for the past 5 1/2 years without any problems until recently. The service man didn't know either and he called a distributor in the area and they told him that these thermostats are not compatible with this type of furnance. He said I have 3 choices: mercury stat, hard wired, or total battery operated. Has anyone heard anything like this before? Is there anything else that could be the problem? Remember the mercury stat works perfectly fine when it is hooked up.

Thanks for any help.

-- Confused (saikofive@hotmail.com), April 14, 2003.

My situation has a lot of similarity with what has been described by many here. When I turned on heater, the blower never comes up. After a while, the heater will cut off itself. Next, I check cooling. When cooling is turned on, the air compressor works fine, again, the blower does not budge.

In the heating case, it is supposed that the on/off is controlled by thermostats. However, since blower does not do it, no hot air realy is delivered to a room where the thermosata is located. The temperature on the thermostate does not change a bit, how is the heater shutting itself off ?

In the cooling case, I did wait for 10 minutes, the blower did not run. I am not sure if I waited enough, the air compressor will shut itself off or not. But as it is on, no cooling is into the house.

The thermostat is a digital one although it is 8 yrs old. Everything worked fine until last winter. One day, the blower did not come up.

Welcom to any suggestion.

-- Jim Mann (xbuxbu@yahoo.com), April 27, 2003.

Jim Mann! You have a problem with the blower motor or the wiring that goes to it. First thing to do is to check and see if you can turn the blower wheel by hand. It should turn easily and free. If it does--the wiring needs to be checked next. You should have more than two or three wires going to it. With A/C the blowers will be two speed [at least] with the slow speed hooked to the heating cycle. The faster/fastest will be for cooling. If the blower doesn't run on either--I imageine the motor is bad. Lack of oil in the blower bearings will cause'm to sieze. When this happens--new motor.

The operation of heat and cooling is different that each other. Fan switches [or relays on the newer computered furnaces] control the heating while the a/c is controlled by a relay independant of the heating circuit. old hoot. Matt.24:44

-- old hoot (oldhoot@shawneelink.net), April 28, 2003.

Here is my problem with my AC: The breaker for the furnace is keeping tripping. I replaced the filter, clean the coil, and unclogged the drainage. When I turn the cool/off/heat to off position, the fan (blower) is on and could not shut off. Can anyone give me some suggestions? Thanks! Jim

-- Jim (pj11022002@yahoo.com), May 08, 2003.

Jim! It appears that you may have more than one problem but just guessin--try checking out the t-stat wires that the red is not crossed with the green. If they are ok [you can disconnect the red rom the furnace and see if it stops the blower] and not crossed the problem is in either the fanswitch or the relay. The fanswitch controls the blower in heating cycle only while the relay kicks the blower on for a/c.

The other option is the pilot light is warming up the fan switch to kick the lbower on. As far as the furnace trippin the breaker--hard thing to guess also. Sounds like lightning may have gotten into your system.

old hoot. Matt.24:44

-- old hoot (oldhoot@shawneelink.net), May 11, 2003.

I'm having a similar problem with my furnace, too. It's a high-efficiency, natural gas, forced air Coleman-Evcon 90 and it's about 8-10 years old.

I just purchased the house recently, so I'm not sure of the history of the furnace. It has worked well for the previous month. For the past couple of days, it has not been heating very well. Upon starting it will ignite and flame for a couple of minutes. When the blower kicks in, the flame goes out and the blower continues to run and force cool air through the house. Every time I power the furnace down and attempt to re-start, it goes through the same process. I have not called in a service person - like others, I'm very reluctant to spend $$$ if it's something that can be easily fixed. I have installed a new furnace filter and cleaned out the drain lines. Any suggestions would be greatly appreciated. Thanks, Jon.

-- Jon (jb64ca@hotmail.com), November 22, 2003.

Hi Guys, Hope you can help, my heater is not working, I have a honeywell 3600 which I installed over a year ago and it worked perfectly, now I can turn on the fan manually but on its own it never comes on. I even raised the temp to 85 and nothing, the tehrmostat shows a flame symbol but nothing happens. Anyone know anything I can check, else should I call a repairman.

-- Dev (dev249@hotmail.com), December 19, 2003.

Hey Dev! IF my memmory serves me correctly that 3600 is digital with batteries. First thing to check is the batteries, if it has'm. The readouts will work sometimes when the batteries don't have enuff juice to kick it on automatically. By switchin the fan on--is a manual operation and doesn't need the battrys for that.

Many othet things it could be but with no more info than you wrote it's almost impossible to guess. oldhoot. Matt.24:44

-- oldhoot (oldhoot@shawneelink.net), December 19, 2003.

As soon as I turn the furnance on the Blower starts running. The blower and burners run constantly. I heard talk about limit and Fan switchs. Can you explain home I can test to verify these are bad? Can they simply be bypassed to for a quick verification test?

-- Marty Smith (video@hiram.edu), January 14, 2004.

Marty! What kind of furnace, how old[approx] andjust a mite more details of the operation if you will. I will make a guess tho--- without knowin anymore about it. If the thermostat is workin properly the problem is in the control wiring. A possible short circuit between the RED and WHITE wires. Try disconnecting the Red wire from the terminal strip in the furnace. This will kill the 24 volt power to the t-stat and will shut the furnace off--that is if the t-stat is bad. Let me know and we'll delve a little more into it. Be careful and don't get into the 120 volts!! These control or t-stat wires are only 24 volts and wont hurt you. old hoot. Matt.24:44

-- oldhootgibson (oldhoot@shawneelink.net), January 15, 2004.

Hi! I hope somebody can help me. It is very cold in Wisconsin. :)

We have a 15 year old Lennox Pulse gas furnace. The heat exchanger was replaced about 4 years ago, due to a recall, and the furnace is serviced every 2 years.

My current challenge is that the heater will work fine for a day or so, and stops. It will not kick in, again, until it is about 50 degrees. We usually have it set for 65-68.

We had the installer/service out here and he checked the condensation line (no problem), read the voltage across the board at the bottom of the front panel, and then went to the 40 year old Honeywell mercury thermostat. He jumped the red to white, and it worked! The service tech said it would need a new thermostat and that would be $165.00. We purchased a new mercury stat($40.00) and installed it. It took me about 1/2 an hour. Everything seemed to work fine for a day or so, then POOF! Same thing....

However, I no longer have to wait for it to get down to 50 for it to kick in. I monkeyed around a bit...If I turn on the fan, turn off the stat, turn off the fan, set the temp to 50, turn the stat back on, turn the stat up to 70, about a minute later the furnace is going, again. This, even when it is only 60 degrees.

It just won't kick in by itself. My husband and I are concerned because we don't know if it will suddenly stop working all together and it is very cold here. After spending money on a service call and cleaning a condensation line that was not blocked, and having to purchase and install a new thermostat, I am so hesitant to contact the same contractor. We are in a small rural area, so there are not many choices (and they might be worse....)

One last thing. The service tech said to set the heat anticipator to .6. Honeywell, said to .4, and the service manual for the furnace says .8 or.9, depending on the valve. I have no idea where the valve is to check the brand, but I set the anticpator to .8 about an hour ago. Could the anticipator setting be the problem? Is it just a coincidence that we are having the same problem, after installing a new stat? ANY thoughts or advice would be welcome. Thanks!

Erin Gjertsen

-- Erin Gjertsen (ergjertsen@centurytel.net), January 19, 2004.

Erin! Without being there to do some testing it's fix'n to be a challange. First thing to do is to locate the gas valve. It will be a little square metal "thingy" with the gas piping attached to it. Wires hooked to screws on top--should be two but could be more depending upon the brand of gasvalve. On the side of the valve will be a little sticker and on that sticker will be an amp draw number. Most of'm I ever saw are in the area of about .4 or so. Set the anticipator of the t-stat to that number. It makes the furnace run longer or shorter cycle--depending the location you set it to.

The problem you have with the furnace is connfusing to say the least. The first thing I'd do is to check the power running to the unit--particulary the ground wire. A loose ground will cause problems llike yours--no sense or reality to anything. The loose ground, if it has one, doesn't have to be at the furnace. It can be in the main breaker box, on the service entrance or on the power companys side.

When you jumper the red to the white and the furnace runs--you have in effect taken out the t-stat of the circuit. If you did not disconnect those wires it probably burned up the anticipator in the t- stat. To jumper any of the wires be sure and disconnect the t-stat.

Red is power to the t-stat, white is the heating circuit [goes to the gas valve, limits etc] Hope this has helped direct you in a way that will fix the problem. old hoot. Matt.24:44

-- oldhoot (oldhoot@shawneelink.net), January 19, 2004.

Hi OldHoot, Thank you, for your thoughts on this! It is perplexing... Although extremely mechanically inclined, I have little experience in the area of heating. I did have college electronics, but that was many years ago.... I will check the valve on the furnace, more carefully, now that I know where to look. The manual(I guess I should have looked at the pictures for where the valve was) that came with the furnace, named two brands that were standard with this furnace. If it was one, the anticipator should be set at .8. If the other, .9 It appears I WAS looking at the valve. There just is not any "brand" on it, so I could not tell which one it was. I will look for numbers, as you suggested. I also tried looking at the name plate on the furnace, but the information did not appear to be on that (or maybe I just didn't know what I was looking for). I couldn't find anything that said amps or A.

Something told me that we should not jump the wires on the new thermostat, so I did not. I am very glad you told me about the anticipator. I wonder what the service man thought he was doing. He had to know that he was going to do damage to the thermostat...All he said, was to make sure the power was off, before removing them or connecting them, that it would burn up the transformer, if I didn't....

Anyway, with the old t-stat, there came a point, where even jumping the wires did not work. The unit still would not kick in. I read everything I could in the service "troubleshooting" book (much requires a meter). I kept thinking something is not getting the message across. Could be a short circuit, somewhere... or some failing controller. I just don't know enough about what controls a furnace, outside of the t- stat. We had men working this summer, rewiring. They were removing the old knob and tube stuff. The hall light appears to be on the furnace circuit, which I thought was strange, but this house is a cobble from 1914. I only found out, because the light went out, when I shut off the furnace. I should have thought the furnace would be on a dedicated circuit. I will check the wiring at the box. (unfortunately, that is in the basement. Hard to see in the dark :)

Lennox's web site, doesn't even mention the pulse furnace. I guess they would like to forget it was ever made...Still, it would have been nice to have a forum or any information on troubleshooting it.

Anyway, I thank you, for taking the time to answer me. It is a puzzlement. If you have any other thoughts, I am all eyes. :)

Have a great day!

-- Erin (ergjertsen@centurytel.net), January 20, 2004.

Erin! Thanks for the update. First off--the furnace MUST be on a dedicatede circuit! I'm not familiar enough with the lennox pulse so can't really know exactly how it's laid out-but--if it has a draft motor it might be a good idea to check the presure switch on it. My gut feelin, tho, is to think a power problem. Ive seen'm not work when on a circuit with other things. These newer, puter'd furnaces are not nearly as forgivin as the old, mechanical ones. If things are not exactly right they just will not work properly--if at all.

The Pulse furnaces were a good advertisin thing but not nearly as feasable as the "old outdated" ones with pilot lights and mechanical switches, limits and such. Very hard to work on and even harder to find somebody who actually KNOWS how to fix one. I wished you were close to me so I could have a crack at it. I don't know it all but kinda know enough to get around some common problems with'm.

Oh BTw--check the grounding of your electrical system. The newer, putered furnaces has got to have the safety ground hooked up. A loose ground wire will absolutely drive you nuts at times too. Keep me updated please. old hoot. Matt.24:44

-- oldhootgibson (oldhoot@shawneelink.net), January 20, 2004.

Hi OldHoot, Just wanted to let you know that we still have the problem, but not as bad, now that I set the heat anticipator to .8 It keeps perfect heat until suddenly, it stops. Sometimes a day later, sometimes 2, sometimes 1/2 a day... If my electric guys are off the next week, due to the snow, I will have them check the grounding, as you suggested. It is probably a short somewhere. I am just so busy with my own business and I don't like to fool around with breakers, other than turn em on and off. That's why we had somebody rewire, instead of me. Easy, but need to KNOW what you are doing...

I guess it is just one of those mysterious things that are so common in the old houses (this one, in particular). I still can't figure out how they got the hall light onto the furnace circuit, but we'll see if they can find the darn thing and get it off. The hall light is on one of those OLD little brown ROUND wall switches and probably should have been replaced anyway. :)

If we ever do find out just what the problem is, I will try to remember to post it, here. Somebody else might have a similar problem, too. 'Til then, we have heat, lovely HEAT! (((Ahhhhhh))) Thanks, for all your help! Stay warm!!


-- Erin (ergjertsen@centurytel.net), January 24, 2004.

Erin! Something I failed to say about the dedicated circuit for the furnace--it MUST be a grounded [3 wire romax] circuit with the 3rd wire [safety ground] installled properly. Keep us all updated please. oldhoot. Matt.24:44

-- oldhootgibson (oldhoot@shawneelink.net), January 24, 2004.

Hi Old Hoot! Well, we are still fighting the Lenox Pulse furnace. Haven't been able to do much at the breaker box (too busy), but we did not see any loose wires at the furnace end of things.

Just thought I would mention that after the heat quits, it will not turn on, again, until the temperature reaches 58 degrees. At that point, it will usually turn on, by itself. If I am impatient, I only have to turn the temperature down to 50, turn it off, and turn it on again. When I turn the temperature back up to 68, it will kick in. Again, only when the temperature drops below 60. Until then, I could spend an hour and it might or might not work, but definitely right about 58 degrees. It seems to stay on longer (like 3 days) if I have the thermostat set above 70, but dang, that is too warm and expensive... At lower temperature, it turns off about once every day (65-67) to 2 days (68-70), depending.

Very perplexing....New thermostat and all...Could this have anything to do with the "limit switch" thingy? It sure seems to be some kind of control issue or a huge co-inkydink. Any other thoughts?

Peace, Erin :) Trying to keep warm, in Wisconsin

-- Erin (eringj@netscape.net), February 12, 2004.

Erin! It sure sounds to me line a limit. I imagine its enclosed in the puter board and not accessable to folks. I'm not familiar with yours but some of'm have [all I've ever seen] have a "draft blower" which purges the combustion chamber before it's allowed to ignite. Could be it's not purgin properly but I doubt if it's the problem. I would say a faulty limit switch. old hoot. Matt.24:44

-- oldhootgibson (oldhoot@shawneelink.net), February 12, 2004.

I am hoping to get an idea of what might be wrong with this furnace. We rent an apt.in an old house. Our landlord pays for the heat and the furnace is his responsibility. Every winter we seem to have some problem or another and have the furnace serviced. This year the heater is shuting off a few times a day or night(in Canada!!) and won't come back on unless someone goes in the basement and turns it off and on. We had someone come last month because the fan or the blower was on but there was no heat---that had never happened before. Unfortunatly someone had gone to reset the furnace before the serviceman had a chance to check it out.That was the fisrt and last time that happened. He said the was a fault in the furnace and not the t-stat---that's what we are thinking because last year if you touched the stat the furnace would shut off.It's an old mercury one and has an arrow which points to numbers(.4, .5etc)don't know what it's supposed to be at. Not sure if that has anything to do with my problem. Any feedback would be great!! Thanks!Jen

-- Jennifer Mahaney (st.holmes@sympatico.ca), February 17, 2004.

jen. have the serviceman to check the flame probe, burners. the flame has to be "proven" before the puter will let the heat cycle continue. the flame probe is a nail like thing that will be located in front of a burner at the opposite end of the burnets [in multi- burner furncace] of the ignitor. the flame has to travel the entire burners to reach the flame probe. itcould be faulty, dirty burners/probe or ---! if the flame is not proven in 7 seconds the ignition module[puter] will shut it down. after 3 attempts to ignite the unit will lock out. re-settin the puter will let the entire process to start all over agin. keep us informed. old hoot. Matt. 24:44

-- oldhootgibson (oldhoot@shawneelink.net), February 18, 2004.

Hi Old Hoot! Just wanted to say thanks, for all your help. We haven't found a new part, yet, but we will replace the switch, eventually. We are selling, anyway, but it would be nice for the buyer to have a furnace that works. :) Thanks, again. Staying warm, in Wisconsin...


-- Erin (eringj@netscape.net), February 19, 2004.

How about AC units?

When I turn the T-Stat on to A/C everything is great. When I turn everything off at the T-Stat and outside A/C won't turn off.

We have a very old T-Stat, the Mercury kind.

The repair guy said the contacts outside were dirty, he cleaned it up and it worked once. Now it is doing the same thing again, 20 minutes later.


-- Mark Powers (mark.powers@tricaresw.af.mil), February 19, 2004.

Mark! The service man is probably correct. The contacts gets pitted and will stick. A new one is about $20 or so. old hoot. Matt.24:44

-- oldhoot (oldhoot@shawneelink.net), February 20, 2004.

I have a problem with my blower. I think it's the motor, but would like some confirmation before I change it. The blower has a hard time starting. You can hear the electrical load and sometimes I have to help it along with my hand. Without any power hand turning the blower is really stiff. Could it be a bearing in need of lubrication or is the motor about had it. The thing in only 7 years old.

-- steve sanchez (stevesanchez@adelphia.net), February 24, 2004.

Steve! I was fix'n to tell you it could be a capacitor [some motors have'm and some don't] but when you said it turns stiff--. The problem is a dry bearing. More than likely you will not be able to oil it and make it work for very long. By the time they are at your stage-it's too late. My guestimation is a new motor is in order. old hoot. Matt.24:44

-- oldhootgibson (oldhoot@shawneelink.net), February 24, 2004.

Thanks for the confirmation. You know how it is, why replace it when all it needs is a little maintenance. I opened a vent in the basement to heat the area up a little. I figure the colder it is the stiffer the bearing becomes. Thanks again.

-- steve sanchez (stevesanchez@adelphia.net), March 01, 2004.

Having similar problem to Annemarie's post awhile back with Lennox pulse furnace. When it kicks in, the blower blows cool air for a minute, then seems to 'warm up' and finally blows warm air until the desired temp is reached. At that time, the damn thing keeps blowing cold air forever, and won't stop even when I turn the heat off completely at the thermostat! I've read answers about turning some internal switch, but where would it be located? I opened up the furnace and all I see are the wires - nothing that could conceivably be called a switch.

Thanks for any help you're able to give!

-- Linda Flowers (anon_incognito@hotmail.com), October 25, 2004.

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