I have a Heil PGAA24C1K1 natural gas furnace with a programmable thermostat, digital type.

The unit cycles on and off frequently when heating, I've done a lot of searching but my problem is different that most others I read.

First, this only happens when it's cold outside, like 25 degrees or colder...
The thermostat makes a click sound calling for heat, the little exhaust blower fan starts, then the three burners light, the flames are all blue, very clean looking now wandering flames etc..

Then after a short time, the blower kicks on and blows warm air into the house. It will run for about 60 seconds, sometimes 45, then the blower stops, then the exhaust blower kicks on again, the fire lights and after a short time, the blower starts again. It repeats this over and over until the room reaches the temp set on the thermostat.

Now tonight I noticed something a little different. The thermostat calls for heat when the temp drops 1-2 degrees below the setting, say the thermostat is set for 72, the rooms drops to 71 and then it clicks and calls for heat, and then it behaves with this cycling on and off (again, only when it's below 25 degrees outside). IF I push the temp up say 5 degrees, move it to 77 and the room is 71 the furnace comes on as it should and heats until reaching the 77 degrees desired temp and there is NO cycling...

I have looked the unit over, everything is clean, all vents inside are open, furnace filter is clean, nothing bad as far as I can tell.

Could this simply be a bad thermostat?

Thanks, Patrick in TN

Need to know more of the t-state.sounds like you need to set the cycle rate on the state or set it for forced air

This sounds like the heat anticipator in the thermostat, Depending on the thermostat, you will find a little scale with numbers from .1 up to about 1.6 and an arrow pointing to one of the numbers, the indicator should be pointing to at least .6 and if that does not stop the problem move it on up to 1.
Now if this is a programmable digital thermostat then you will probably have to read the instructions on how to do it.

Please let me know if this helps you.

Hi Greg, the thermostat is a Ritetemp GPMG8050C, got it at Lowe's for like $30.00

There aren't too many settings,
The differentia is set on MJ1 2 degrees
It's on 12 volt
And set on gas,
It's on Normal mode (not pump)
That's all the settings there are.

Should I get a thermostat that has more settings?

Don't know much on the settings on that. Not big fan of the ritetemp. Go for a honeywell vison pro or fouse pro. Whiterodges makes a good state to

Hello, I installed a Honeywell RTH6300B from Lowe's. I still have the same problem.
What should I look at now? High limit switches?

Stumped...

Try sealing the hole behind the thermostat where the wire comes through the wall.

Hi, I did seal that hole tight so no air is coming in from behind the thermostat.
Now it's 40+ degrees outside and it runs fine. I'll watch it tonight and see if it does the short cycleing again.

I forgot to mention, about 2 years ago I had a HVAC guy out, he said that a "part" had a crack in it and that there are two of this "part" and he was to catch it in the act to determine which one to replace, He said it was $400+ dollars so he wanted to make sure he got it right.

I can't recall the name of the part he said... UGH!

Thanks
Patrick

Hmm

Check for the basics. Are drain hoses clear(not plugged at all). Clean flame sensor. Check vent for outside obstructions.

Check your return air for proper sizing, dirty filter, or dirty coils that may be restricting the airflow possibly over heating your chamber limit allowing it to cycle on and off as the heat exchanger cools and or overheats you might need to add a fresh air duct or resize your return...