Central Heater "Short Cycling"

[Russell]

HELP!!
My Concord gas central heater is driving me crazy!!! It is a model #RGC80A078010-1B that was installed approx 7 years ago. Has worked without problems until this year. Now it will cycle on and the burner will light and burn for several minutes to heat the house up, then the burner goes off (Thermostat is still calling for heat) for approx 1-2 minutes then relights for 4 seconds and goes off for 15 seconds and then relights for 4 seconds and then goes off for 15 seconds. It will do this anywhere from 4 to ten times then cycles off and the blower will cycle off. If you look at the thermostat it is still calling for heat. After 2-3 minutes it will cycle on and go through this process again and again until the house is warmed up to set temp.

I have replaced the thermostat 3 times (at service techs recommendation) and was told if that didn't fix the problem then the control board needed replaced which I did tonight with no improvement.

Looking at the diagnostic code sheet that came with the new circut board I have both diagnostic lights flashing alternately which indicates the system is in "Watchguard" mode and that the burners have failed to ignite.

I think that one of the safety switches is not working properly but I don't know where to start looking and how to check for proper switch operation and if the can be tested for proper operation. The local service tech said that the new board would fix the problem and is now at a loss for a cause.

Any help would be appreciated. Thanks. :?

[roger g]

And this is gas or oil furnace? I would think gas but might not be.
High efficiency?
roger

[Russell]

It is a natural gas heater and has an 80 Plus rating. :)

[roger g]

It will be loaded with sensors any of which could be faulty. Check to make sure that the intake air and the exhaust are clear. We would actually disconnect these pipes at the furnace and run the furnace Yes I know that exhaust is coming into the house but remember these are very efficient and very little carbon monoxide. If you say it only runs for 4 minutes and when you disconnect the pipes you run longer than 4 minutes then you have found the problem A few minutes exhaust won't hurt anyone. You might have a cracked heat exchanger which is recirculating exhaust.. Check the condensate lines to find out if itis removing all the water. If it back up it won't run.
Lots of stuff to go wrong.



roger

[Sparks]

Could be a few different problems. Possibly hi-limit safety opening control circuit due to a problem with the hi-limit or because there actually is a high temperature condition that it's sensing. Gas furnaces can be extremely dangerous as I'm sure you realize and if you have no idea what to check it sounds like you should call a company that does. A quick look at the schematics should point a service tech in the right direction on where to start troubleshooting and not just guessing and wasting money throwing parts at it. Bad heat exchangers can cause high temperature problems and can also cause death due to co poisoning. There are just too many variables and risks in attempting to solve this problem on the internet. Not trying to be a jerk, just honest. Just my opinion. Also, you might want to stop listening to your service tech as he is obviously wasting your money.

[Russell]

Thanks for all the help, I will be calling a different tech to see what the problem is. Just thought I could narrow the problem down and stop throwing money at the problem like you said. Thanks again. :D

[rabadger]

could be venter pressure switch or a limit switch. The blinking lights should tell you whey it is failing. You have to have the codes that tell you.
The number of times the light blinks corrisponds to the failure.

[Dragon]

The codes for the lights should be on the inside of the service panel if they arent on the outside.