I bought this Noma thermostat and the heat stays on, no matter what. Even if I detach the front plate the heat remains on. When I reinstall the old mercury swtiched thermostat it works fine. I have a 2 wire hydronic heat system. Can anyone tell me why the heat stays on?

Any advise will help. Thanks so much.

Your new thermostat is probably not compatible with a two wire system. You might have to pull a 3rd wire for proper operation.

It could be a bad thermostat. Before our H&C expert, Northern Heat , went AWOL, he used to suggest NOMA's were junk.

If it powers up on 2 wires, it should work.