# Comfortmaker heating problems



## nomad591 (Jan 12, 2004)

I am having big heating problems with a mod #GUI100.
1. call for heat, evac fan starts and everything goes well.
2. unit running, high limit kicks off gas, 
3. unit cools down 
4. evac fan starts again, flame starts after 3 to 6 seconds gas shuts off.
5. it does this over and over until unit shuts it self off for too many restarts.

No vent dampers, no failure codes until too many restarts, has a white rogers 50A50-142 control unit (2 years old) been replaced, 

It only does this when it gets really cold out and the unit has to work to keep the house warm.

Any help would be great.
Gene


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## Bjd (Dec 19, 2003)

Unit should never shut down on high limit, possible problems with filter/ac coil.

Your duct work may be sized wrong, as not enough air flow over the exchanger.

Bernie


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## Steve Wiggins (Jan 17, 2004)

How do you know the high limit is opening?


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## Guest (Feb 15, 2004)

*duct work*

is it better to have duct work (heating and air vents) in the ceiling or floors


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## Guest (Feb 15, 2004)

One thing you may want to check is a cracked exchanger...open limit will occur when the system runs constantly as it continues to burn to keep up. this will not always trip roll out switch if the crack is minimal. but you may get many different error codes..just another thing to look at


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## Guest (Feb 26, 2004)

nomad591 said:


> I am having big heating problems with a mod #GUI100.
> 1. call for heat, evac fan starts and everything goes well.
> 2. unit running, high limit kicks off gas,
> 3. unit cools down
> ...


I am not familiar with the model number is this a 90 percent unit. I have found the secondary heat exchanger plugged and cause the same problem.Pull the blower out and put your head in the furnace there is a coil like a radiator if this is plugged blow it out with a compressor.


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