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Nest/Furnace troubles

Community Member

I’ve had a nest gen 3 thermostat for a little over 1 year that was installed with a new AC unit. I’ve consistently had the E74 error shown intermittently and sometimes can eliminate this by testing the fan. Lately, this hasn’t been working. The furnace will turn on to heat the house but the burner won’t ignite and the system eventually turns off without heating. I had an hvac tech come out after getting this error in November and a fuse in the furnace had blown. After this was replaced, the furnace worked until a few days ago. Now, it won’t heat and I periodically get the E74 code, but it also goes away intermittently. Does this sound like a faulty thermostat or some kind of burner issue with the furnace? 

Thanks in advance for the input!



Silver Product Expert
Silver Product Expert

If you go to the furnace there should be a little lens that you can look thru to see led lights on the control board.  Look at the blinking lights and count the number of flashes usually there are 2 led lights.  Then look for the decal that shows what the codes mean.  It will say something like led 1 flashing, led 2 on means high limit etc. Then you will know if it is a furnace issue. Sometimes you have to take the cover off the furnace and the decal is on back of the cover.  But with cover off the door switch shuts off power to the furnace so the flashing lights will stop. You just push in on the switch holding it as it tries again to fire up and watch the led lights for the error code.

Houptee -- NJ Master HVAC Licensed Contractor