An old 240V in-wall heater in my house has recently been spontaneously turning itself on. We don't use the heater (we have a furnace), so we were pretty bummed because there's a couch right up against it, and I have a friend who lost a house to fire due to heater + couch.
Anyway, I shut down power at the breaker box. Meanwhile, the heater appears to have an integrated single-pole t-stat that, when the knob is turned all the way down and clicks off, still has about 18V; if the knob is turned up and clicks on, there's 120V through its entire low-to-high range.
My understanding of things electrical is elusive: electrons are hard to see and move fast. So, my questions are:
Is it normal to have 18V even if the t-stat is turned all the way down? Why would you have the t-stat on a separate 120V circuit? Or is this an indication of a short circuit?
Assuming the t-stat failed, how did it do so in a way that was randomly causing the heater to run? The last time it came on, the knob was all the way down and the house was at least 65 degrees. Also, it hasn't been coming on when it's 50 degrees in the morning.
Finding 120VAC inside a north American 240V appliance is normal, since both wires are hot, 120V to neutral/ground, 240V between each other. Not sure what the 18 volts are doing there though, need more info. Without a manual you diagnose this stuff by figuring out how it should work and comparing that to how it is working.
The 18V comes off the low voltage control transformer. You didn't cut the power to that. You probably cut the power to the heating elements only. The control circuit may be on another breaker. But if you're not using it, switching off the 240V breaker should do it.
And are you sure that's the right thermostat?
yes two legs equals 240v. I agree with Hess that the t-stat is probably powered off of another circuit
I doubt that there is a low voltage section in a wall heater. If you are measuring from line to ground, it will give 120 volts. If you measure line to line you should get 240. Without looking at it, I can't explain the 18 volts. The best suggestion I have is either replace it, or disconnect the power at the breaker if you are not using it.
I found a separate (120V) circuit on the (poorly labeled) breaker box for the t-stat. Thanks
