Thermostat causes breaker to trip when heating turns on

Safety first: This involves potentially serious electrical faults. Turn off the breaker and do not repeatedly reset it without finding the cause.

Steps to diagnose tripping breaker:

• 1. Inspect thermostat wiring:
  • With power off, remove the thermostat.
  • Check that no bare wires are touching each other or the metal back box.
  • Ensure line and load conductors are correctly placed in their terminals.
• 2. Disconnect load:
  • Disconnect the heating load wires from the thermostat.
  • Restore power and call for heat.
  • If the breaker no longer trips, the fault is in the load or downstream wiring.
• 3. Test heating circuit:
  • With power off, measure resistance between load conductors and earth; low resistance indicates a fault.
• 4. Check circuit rating:
  • Confirm the total heating load does not exceed the breaker and thermostat ratings.
• 5. Do not bypass protection:
  • Never replace a breaker with a higher rating to stop nuisance tripping.

When to call a professional: Any recurring breaker trip on a heating circuit should be investigated by a licensed electrician or heating specialist.