I have a model GMNT080-4 condensing gas furnace. When the weather outside is about 25 degrees and higher the heater kicks in and heats to thermostat setting perfectly. When the outside temp gets colder than about 25 degrees the heater kicks in but will not heat to the thermostat setting. Instead of heating to 74 degrees thermostat setting, the heater will kick in at about 62 degrees and never get the home above 67 degrees. [B]I want to know how to get this heater to keep our home at thermostat setting when it gets very cold outside.[/B] I had two "professional furnace technicians" look at the furnace: The first one did the standard checks, burner, drain, exhaust, etc. etc. and said it should be working fine now. There goes $100. The next one told me I needed a new control board - that would really fix it. There goes a few hundred bucks more. That did nothing to fix the problem. So, what do you think is the problem and how do I resolve it?

The furnace starts up normal... Fan-flame- sometimes blower... The blower will turn on/off 5-10 times threw cycle and u can hear a clicking while it does this... Furnace will heat up and shut down normally... No blinking lights .... It does not do this everyday... Seems the colder it gets the more it happens .... Plz help I have a 3 yr old and wind chill is suppose to be -20 tonight