While working in the garage yesterday, I noticed that my furnace is
cycling on and off *constantly*. I hear the gas jets kick on and they
burn for about 15 seconds, then shut off. About 30 seconds later it
repeats the process, over and over and over again. Only occasionally
did the blower kick on where hot air was pushed through the house.
I don't know a dang thing about furnaces, but this can't be normal
functioning of the furnace, can it?
Nope. Not normal. If you know nothing of furnace repairs call a reputable
repair company. It could be one of several things, but most likely a bada
thermo-couple fo some sort that is causing the burner to shut down before
the blower comes on. I'd get it looked into before the really cold weather
Nope, definitely not normal. Could be a number of things (bad flame sensor
Here is some troubleshooting help -- however, gas isn't something for the
untrained DIYer to mess with. I'd recommend you call a professional.
Not enough info to even begin to tell you where to look, but as others have
suggested, if you are not familiar with the operation and sequence of proper
events, call a company, and make sure they are licenced and insured.
In general, there are two limit switches in the furnace plenum: the fan
limit, and the gas solenoid high heat limit. It is obvious, in your case,
that the fan limit is set too high and the heat in the plenum is rising
above this setting to a point that the gas valve high limit is tripping the
gas valve closed. When it cools, it turns the gas valve back on again and
this cycle repeats. Find the fan limit and set it lower, maybe around 140
degrees and see if that will make a difference. From your description, it
is obviously not the room thermostat. If you cannot change the settings on
the fan limit switch, maybe it is broken and needs replacing.
suggested, if you are not familiar with the operation and sequence of
events, call a company, and make sure they are licenced and insured.<
Called several over the past few days. Most have not even bothered to
return the phone call, while the others say it'll be the end of next
week before they can make a service call.
if that will make a difference.<
Anywhere online where I might see a photo or diagram of what the fan
limit looks like? I'd rather attempt a simple fix first, and if that
doesn't work, wait ten days for a pro.
Yeah, I don't think it's the thermostat, otherwise wouldn't the blower
be kicking on and off too? I noticed today that when I turned the
thermostat down (from 72 to 68) the cycling stopped. But as soon as I
set it back to 72, it started continuously cycling again.
Depending on your part of the country, thats normal for this time of year...
Also, since the election, this trades business has taken off for the better
and you should, since if you dont know what it looks like, or even if you
have one, you can create more damage than you have now.
Not all of those old Carrier/Payne units had them.
Particularly since the blowers were on timers that were hardwired into the
Depends onthe thermostat you have. While the least likely item would be the
stat, its possible you are #10, and 9 out of 10 issues are not the
thermostat, perhaps your numbers up.
Wait a bit, get the tech to check it.
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