Dettson Control / Thermostat Overshoot

Boiler runs continuously and overshoots the thermostat setting

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Safety Warning

This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.

If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.

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Possible Causes

Stuck thermostat relay, Miswired thermostat to Dettson boiler, Faulty room thermostat, Incorrect control parameters

How to Fix / Troubleshooting

Safety: Turn off power before working on low-voltage wiring.

  • Check thermostat: Verify the thermostat is set correctly and not in a constant ON or override mode. Replace batteries.
  • Test thermostat circuit: At the boiler, temporarily disconnect the thermostat wires from the Dettson control. If the boiler stops, the issue is likely in the thermostat or wiring.
  • Inspect control board: If the boiler continues to run with thermostat wires removed, the internal relay on the control board may be stuck and will need replacement.
  • Review settings: Ensure any built-in room sensor or setback functions are configured correctly.
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Repair Difficulty

Medium 3/5

Required Part

Room thermostat
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