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Mini Boiler wont shut off

I have a 20-year-old Wright-Hennepin Mini-Boiler model EMB-9. Last year I installed a Smart Thermostat and it ran all winter with no issues until the end of the season when I noticed the heater did not turn off when it should have.
Even with the thermostat disconnected, it still will run.
I now manage it manually, fortunately, I heat with wood as my main heat source.

Suggestions to start troubleshooting?


  • Jamie Hall
    Jamie Hall Member Posts: 23,322
    If it still runs with the thermostat disconnected, try disconnecting one of the thermostat wires at the boiler. If that stops it, you have a short in the thermostat wires.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • GroundUp
    GroundUp Member Posts: 1,908
    That boiler was built by Electro in Monticello. If you disconnect the thermostat wires at the boiler and it still runs, it's probably time to start looking at a replacement. The controls in that unit are pretty tough to get anymore, but Dean or John at Electro may be able to find you one or even a retrofit if it's necessary.