Heater quits in middle of night

Old 11-15-19, 01:03 PM
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Heater quits in middle of night

I have a weathermaker 8000. The thermostat is set to 75. When we wake up in the morning, the unit has cut itself off. After a reset, the furnace turns on just fine for the rest of the day. The code it throws is a 21 ( Gas heating lockout, control will NOT auto reset). I have had the service guy out and cleaned the unit. It still happens and he wants to replace the motherboard (424.22 dollars worth) He did say that was all that was left that it could be?? Odd thing is that when I set thermostat to 77 for the day and night it never kicks off. I did this for three days during a cold spell and after the cold spell left, I turned it back to 75 and it kicked off after about 5 hours of running without issue. So, do I allow the motherboard change, since it is just a hit and miss option?
Old 11-15-19, 04:36 PM
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I wonder if it's the thermostat since it's the only thing that can sense or measure temperature. The next time the furnace quits working see if jumping it out at the furnace (taking the thermostat out of the equation) gets it working.

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