Furnace keeps turning on and off

[mrstrictlygm]

My furnace keeps turning on and off, I usually notice it at night. It will kick on, run for a few minutes then shut down. Then after a few minutes will kick back on again. I had a similar problem last year, but alot worse. I think it turned out to be a dirty flame sensor, I cleaned it off and it seamed to work fine. Could it be that this sensor needs to be replaced or should I keep cleaning it off? How much are these flame sensors? My furnace is in my 5ft crawl space that has pee gravel, I do have to change the air filter pretty frequently because of the dust from the gravel, could this dust effect the flame sensor? Any help is appreciated. Thanks in advance.

 

[HVAC Phil]

Could be the flame sensor, could be alot of other things too. Limit switch, inducer motor pressure hose plugged, t-stat, etc.

 

[hydramatic]

count the light blinks. thats the code..3 blinks then 4 blinks code 34. google that. good luck

 

[Falcon67]

If it the burners or the blower? Our old house furnace had issues with the firebox limit switch. The old one went out and the only replacement (furnace was a 1976 model) was very sensitive. Air return was at floor level and on cold days, the return air would cool the firebox enough to shut down the blower. The burners would still be lit. It'd build up more heat and the blower would kick on again. Had to tweak it between mild weather and cold weather.

 

[Mmfh]

Are you sure the thermostat isn't calling for heat? House is just cooling down to the point that the stat wants heat again?

Mine does that all the time and it bugs the hell out of me, I think my house just cools quickly and the stat is calling for heat.

Mm

 

[matouse3]

Check the filter! Mine did this and I found that I had an unusually dirty filter and the kick back was shutting down the system, but the thermostat was calling for heat.

 

[theoldwizard1]

Similar problem and installation to OP. Horizontal furnace in (poured slab) crawl space.

On bitter cold days/nights (below zero) the over temp (limit) switch would turn the furnace off before the thermostat. As soon as the limit switched cooled down, it was back on again until it overheated.

Furnace guy lowered the pressure on the regulator (little impact) and made certain the blower was at max.

Luckily, we don't have temps like that very often.

 

[6768rogues]

It is called short cycling. It could be a bad thermostat, pressure sensor, weak fan, bad limit switch, obstructed airflow, obstructed combustion air inlet, or a simple adjustment, among other things. If it is not the filter or something that you can easily find, the problem should be diagnosed by someone who knows what he is doing or else you are taking a shot in the dark.