My living room is heated by two electric baseboard heaters controlled by a single thermostat. Earlier this week, I noticed that the room was much warmer than it should be, and figured that the thermostat had gotten stuck again*. After turning the dial failed to produce the "click" of the switch turning off, and dialing the temperature all the way down didn't cool the room, I assumed the thermostat had failed and replaced it. However, the new thermostat shows what appears to be the same behavior: when the thermostat turns off, the heaters don't turn all the way off.
- Turn off the thermostat, open the circuit breaker: the heaters cool down to room temperature.
- Close the circuit breaker: the heaters stay at room temperature.
- Set the thermostat to 70F: heaters warm to around 200-250F.
- Room reaches 70F: thermostat turns off (I can hear the click), one of the heaters cools to around 110F while the other cools to around 160F.
- Turn the dial all the way down to "off": heaters stay the same temperature.
Both the old thermostat and the new one are simple bimetallic-strip switches. I tested the old one with a multimeter, and it switches between infinite resistance when off, and zero resistance when on.
Any idea what's going on, and how I could troubleshoot/fix it?
* The switch in the old thermostat occasionally got stuck, not turning off until much warmer than the setpoint.