My fan in the bathroom is constantly running no matter what position I put the switch to.

The switch looks like this:

enter image description here

And there is some other controller that I don't understand what it does (never used it before):

enter image description here

Can someone please tell me, how is it possible that the fan keeps running even if I put the switch in the off position?

Is it probable that it has some internal sensor and that sensor turned it on?

Also, did someone see that "Thermolec" controller before and can point out to me what it does?

This is the model of the thermolec controller:

enter image description here

And this is the fan case (sorry I can't get to the fan right now because my hand is broken. I'll need help):

enter image description here

Thanks in advance for your kind help.

P.S. There was a power outage insident recently. A lightning strike hit the house and there was no electricity for 3 days in the neighberhood because 2 transformers were blown out. That's when the problem started. It might be a coincidance because a real brutal heat wave has also arrived at the same time and the electrical generator that the State Electrical company has put infront of my windows doesn't help with dissipating heat. lol

  • 1
    Can you give us model numbers for all the things involved? (fan, switch, thermoelec controller) Commented Aug 4, 2017 at 0:57
  • 1
    We'll need the make and model of the fan and wall-switch too Commented Aug 4, 2017 at 1:11
  • 1
    You'll have to turn off the bathroom breaker and pull the bathroom switch out to see the model number (it may or may not not be an ordinary switch). Also, the fan may take a bit of work to get to, but should be accessible from the attic/ceiling space above it... Commented Aug 4, 2017 at 1:25
  • 2
    I think I know where @ThreePhaseEel is going with this, but curious, did the wall switch always work (to turn off the fan) in the past? If you are taking the wall plate off (and turn off breaker power) you can always check the switch with a ohmmeter while you are in there. It is not impossible it welded or broke in the on position.
    – noybman
    Commented Aug 4, 2017 at 1:33
  • 1
    Here is the data sheet from the manufacturer web site for the FC-FER-6-1.5-120. thermolec.com/_documentationcache/… ![enter image description here](i.sstatic.net/0qo8f.png)
    – Michael Karas
    Commented Aug 4, 2017 at 9:52

3 Answers 3


The thermolec is a make up air duct heater , the lightning strike may have damaged the control board is the occupency sensor causing the fan to run as long as there is power. I would turn the breaker off pull the controller (switch) and disconnect its power if the fan stops you know where the problem is the switch. If the fan continues to run with the power restored and the switch disconnected the thermolec duct heater may be controlling it and that would be the next item to remove power from the controller (with the power off). I would guess the occupancy sensor part of the switch failed.

  • I switched off the breaker for that switch and the propeller stopped working. Now I need to replace the switch I guess since it's established that the switch is faulty? Commented Aug 4, 2017 at 18:37

Remember start simple."lightning strike, power outage." Good chance something fried. If you smell any burnt electrical follow your nose. The Middle switch looks a little funky in the picture. Everyone else is overthinking it like engineering types tend to. Mechanics use a little common sense first😎


It's getting a constant ground so look at the fan power switch being shorted. Power looks for a ground, normally the switch turning on gives it a ground and turns on the fan. Power sits waiting for the ground but if the on/off switch melts due to a surge it may act as if it's always on

  • How do I get neg feedback for saying a shorted switch or do I speak to simply for the electrical gurus to understand. The switch is bad Jenia. Easy replacement👍🏼
    – Derek
    Commented Aug 4, 2017 at 20:12

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.