My furnace has been behaving strangley lately. It starts up, runs for
a minute or two and stops. A few seconds later it does it again. It
does this 3-4 times before finally running until the selected
temperature is reached.
I thought I'd ask for your opinion on what the problem might be before
I get screwed by the nice furnace repairman who used to be a surgeon
but quit because he wasn't making enough money!
Dan... I had the same problem and it was explained to me.... My furnace
would run its cycle and after about two minutes of finishing this cycle it
fired up again and then it quits a minute later....He fixed it and gave me
...What happens through a normal heating cycle is the thermostat on the
wall in the house gets cool & tells the burner to fire up...so it does
this.....after reaching the proper temperature inside the furnace the burner
tells the fan to kick in...the fan kicks in and distributes the heat all
over the house and then the thermostat tells the burner that it has reached
its temperature so the burner shuts down....the fan keeps running to cool
the burner as the burner tubes must be cool before shutting down...there is
a heat sensor that tells the fan to shut off when the burner is cool...then
the cycle is over. Until the thermostat gets cool again.
Your problem is that the heat sensor on the burner is telling the
fan to shut off too soon.....as a result, the residual temperature of the
burner builds up and tells the sensor it's still too hot which fires up the
fan again to cool it down a little more....hense the fan firing up and
Solution....turn down the setting degrees of where the fan should kick
out after the burners are shut off. This will allow your fan to run a little
longer after the burners have shut down and prevent the quick start ups for
no apparent reason. The adjustment is usually located under the small
plastic panel where you have the option of pulling a switch out for the fan
to run on auto or pushing the switch in for the fan to run on manual. It is
located behind that box. Hope that was of some help... Jim
I had a similar problem , the flame sensor indicator was dirty removed it
wiped it off re-installed and it worked fine, that was then I have a new 2
stage furnace with a 16 seer heat pump. Its great!
Can you tell us:
When it runs, does the fan come on?
Do the burners really light?
Has anything changed- perhaps a thermostat?
As some of the posters havee mentioned, this could be:
A Flame sensor or limit switch.
If it were the limit switch, the fan would continue to run until the
chamber cooled enough. If you are experiencing a problem where the burner
is cycling several times (and you don't have one of those new super
effeciency jobs) during the fan cycle, make sure of the following:
1) All of the return air vents are open unblocked
2) the air filter is clean
The guy that suggested messing with the limit switch- well I wouldn't
recommend it. One of those settings has to do with making sure that the
thing doesn't run until it melts.
This could also be the thermostat, but a little more unlikely unless it has
been recently changed. Does this happen if the t-stat is turned all the way
down?What kind of t-stat do you have?
If the flame sensor was bad, the burners should not light ( or should go
out within 10-30 seconds).
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