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Air Handler Suddenly Wont Shut Off
Our problems started after a rare winter thunderstorm came through. There was a lighting strike pretty close by. I noticed the Nest E showed an error "no power on R wire" even though I was getting 27v at R&Y1 and R&W1. Called Nest and they said the base is bad. I also noticed the heat was not shutting off. We have a Laars Endurance propane boiler that feeds a First Co. MBXB air handler in the attic. A second zone is baseboard hot water downstairs but rarely used.
Luckily I had an extra brand new Nest E handy. I swapped out the base and tried both Nests on the new base. Both were reading voltage now. I still could not get the boiler or the air handler to shut off. The 4 tstat wires come from the First Co. air handler in the attic. From there, a wire runs to the boiler. It looks like the tstat controls the air handler which then controls the boiler or AC in the summer.
I had to turn off the circuit breaker to the air handler which then allowed the boiler to power down. It seems that the boiler is still working for domestic hot water. I'm leaning towards the First Co. air handler control board CB201 being the culprit but I'm not an expert. Anyone have any ideas? Thank you!