Thermostat – How to Verify a Resistive Load Thermostat is Dead

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I have an electric heater, connected to a resistive load thermostat (240V). Yesterday we found the thermostat apparently totally dead (display off, etc). I've checked the breaker, of course. (There is no battery in this type of thermostat.)

The thermostat is wired like this:

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I have a decent multimeter. How can I verify that this is indeed a problem with the thermostat and not possibly with something else (ex. power supply, wiring to heater, or the heater itself). If it's relevant, the heater is a simple convection electric heater with no controls.

Thank you!

UPDATE: Finally, it turns out that the (certified!) electrician completely botched the wiring the heater itself. When I opened up that junction, the wire just popped right out. I connected it properly and securely, and the problem appears to be resolved.

Best Answer

I would test the system as follows:

  1. Turn of power at the breaker/fuse box
  2. Disconnect the two wirenuts going to the wires coming from the wall.
  3. Directly connect together those two wires, using a wirenut.
  4. Restore power at the breaker/fuse box.

If the heater comes on at full power, then the problem must be the thermostat. If the heater doesn't come on or at low power, then the problem is elsewhere. For example, if the heater element has failed open, then no power can flow and the thermostat would not get power.

After testing, be sure to disconnect power at the breaker/fuse box. Do not try to use the breaker as a switch as most are not rated to be operated many times.

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