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airheatman, HVAC Technician
Category: HVAC
Satisfied Customers: 8326
Experience:  Furnace, A/C and heat pump specialist.
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Furnace comes on even though thermostat is "off". The only

Customer Question

Furnace comes on even though thermostat is "off". The only way to turn furnace off is to turn gas valve off and disconnect fan at electrical outlet Replaced thermostat with no change. The main control board is Electron B89322B. Thank you
Submitted: 2 years ago.
Category: HVAC
Expert:  airheatman replied 2 years ago.
Hello. My name is ***** ***** I'll do my best to help. Let's get started and see what we can do.Disconnect the control wires from the board and see if furnace goes off. If not board is bad and will have to be replaced.
Customer: replied 2 years ago.

Isn't disconnecting wires from the board the same thing as turning new thermostat off?

Expert:  airheatman replied 2 years ago.

Not really.THere could be a nick in wire in between causing R and W to make an d bring on furnace.That is why I say at control board.That eliminates any external influence

Customer: replied 2 years ago.

HI Tim,

Thank you very much. Something just came up that I have to leave for a couple hrs. I'll try your suggestion tomorrow.

Expert:  airheatman replied 2 years ago.
I understand. We can go from here.