Aire-Flo HC unit not keeping up with thermostat when outside temps are below 0

My 8 year old high efficiency furnace does not keep up with the thermostat when the temperature outside reaches 0 or sub zero. It seems to stay 5 to 7 degrees under the set temp, sometimes not responding for hours. I've had a "professional" the same wonderful people who installed the unit out 3 times. Each time they've looked it over, cleaned it, and of course charged me -- never solving the problem. Basically the guy made the brilliant statement, "There's nothing wrong with your furnace sir." Really? Any help, or insight would be appreciated.

Aire-Flo
Model CA036A862MC

 

Furnace is undersized? Furnace is underfired (professional needs to check gas pressure in and out of gas valve both running and not)? Does the furnace stay running 24/7 when it can't keep up (burners continue firing)?

 

Shouldn't be undersized it was installed when the house was built. Doesn't stay running, shuts on and off, but never brings the room temperature up to the request from the thermostat. Example: room temp is 68 and thermo is set to 72, furnace sometimes won't kick on for many minutes, then when it does, it runs, but never long enough to get room temp, then just shuts off.

 

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What percentage of an hour are the burners off?

Your furnace probably has diagnostic lights that will disclose the reason the burners are shutting off. Usually they are visible on the ignition control module, sometimes visible through a viewing port on the door of the fan compartment.

Usually there is an index describing the meaning of the diagnostic codes on the inside of the fan compartment door.

Look for the diagnostic codes when the burners shut off and post the explanation for the code here.


The usual reason for burners shutting off is that the furnace is overheating and shutting off on the limit switch. The most common reason for that to happen is that something is impairing the air flow through the furtnace that strips away the heat that's produced.

Check to be sure that the cold air returns to the furnace are unobstructed and that all the warm air vents are open. Check to see if the filters are dirty or plugged.

Let us know what your find.

Your repairman should have checked all that for you of course.

 

Do you have a heat pump with gas aux heat? I would check what SP suggests.