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Regan Land
Regan Land, HVAC Technician
Category: HVAC
Satisfied Customers: 677
Experience:  Over 20 years of experience, NATE Certified, Licensed HVAC Contractor, Certified IAQ Specialist
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Furnace not reaching the temperature set on thermostat

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Furnace will not get up to temperature set on thermostat. Sometimes it just blows cold air. The gas does not come on.

Let's try this: Leave the thermostat calling for heat, then go to the furnace and unplug it then plug it back in. Now, watch the stages carefully and tell me what it does.

It should start the induced draft motor (small motor in the burner compartment), igniter should spark or glow orange, burners should fire, blower should come on.

Customer: replied 7 years ago.
ok the heater went through all stages and started.
Okay, have you noticed it will run for a while and then shut off?
Customer: replied 7 years ago.
it will run till it reaches temp.
Then it will give you a problem next time it starts? I'm sorry, I'm just a little confused.
Customer: replied 7 years ago.
the only way the heater will run hot is to go outside and turn it off then on.

Okay, I see now.

Most likely the system is going into lockout. Next time this happens, look through the little quarter sized sight glass in the bottom panel. There will be an LED flashing a code. Count how many flashes and let us know.

Customer: replied 7 years ago.

The light blinks one time when heater stops.

Okay, 1 flash indicates an ignition failure lockout (tries 3 times than locks out). It is strange that it will start and heat the house after you reset it, but it could be that the flame sensor isn't sensing flame every time.

First, lets try cleaning the flame sensor with steel wool to eliminate this as a possibility. See picture below:


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