[joerobbi]

It won't do anything, not even a click. Board LED is constant red. Verified 120V into transformer, 24V out. It's only sending 16V to the thermostat (Red), and that 16V is coming back (white). Disconnected and shorted R->W, no change. Verified continuity on all switches. Reading 0V at inducer blower. I'm thinking bad board, since as far as I know, it should be 24V to and from the thermostat. Any other ideas out there?

 

[beenthere]

Check that heat exchanger for cracks or popped crimp rings before investing money to replace the board. GMPs are know for popping crimp rings.

 

[NiNe O]

What is voltage between r and c, w and c.