I bought my house with an electric furnace, brand is Nortron. The following is the exact situation:

  • Thermostat is set to 18 Celsius.
  • Air temp (from thermostat) is 21 Celsius. So furnace should not be running.
  • Thermostat is only set to heat mode. So no AC.
  • The duct above the heater is hot. Way above the duct, it is saying 40 Celsius.
  • No Fan of course as current temp is greater than thermostat.

Clamping an amp meter on the furnace breaker is registering 40 AMPS.

After fiddling with the switches (there are 3 switches), didn't really change the settings, just flip, then flip to original/default position, amps is now 6.

What is scary is I got an electric bill that is 200 dollars more than what I'm used to, so this has been happening for more than a month. Since it was summer last month, 100% sure thermostat didn't trigger. Just that it is generating this heat for no reason at all...

What could be causing this? I'll gladly provide more context if needed. For now, I turned off the breaker to avoid burning more money.

  • If you measure between R and W on the thermostat, what voltage do you see? (Good is 24-ish volts, bad is 0-ish volts). Sep 21 '21 at 19:40
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    Could be a few things, perhaps a bad contactor (stuck), or maybe a bad control board. I don't think there's any way for the thermostat to cause this. If the furnace isn't running, you should have virtually zero amp draw....just enough to run the transformer, which probably couldn't even be measured. ....This is a fairly dangerous situation: You have electrical resistance heating that's on with no air flow...not good. Sep 21 '21 at 19:49
  • Heater should not be on without airflow. My guess the controller broken
    – user263983
    Sep 21 '21 at 22:00
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    Can you post the wiring diagram for your electric furnace please? Sep 21 '21 at 23:52
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    Turn its breaker off until you can find the problem, that may save you enough to take someone special out for a nice meal and have change left over.
    – Gil
    Sep 22 '21 at 1:16

The contactor is probably stuck closed. You should shut the breaker off immediately to prevent a fire. There's a high limit switch but that won't do any good if the contactor is mechanically stuck closed.

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