We live in a two bedroom town home, and within the upstairs bathroom, an exhaust fan is located in the ceiling (but not above the bath tub/shower). There is a wall switch containing 3 switches: one switch is for the "primary" light, the second switch is for the fan, and the third is for a "heated" light (we rarely, if ever, use that).

Recently, we needed to have some repairs done to or roof, and it seems that ever since then, the exhaust fan is constantly running. The switch for that fan does nothing to turn it off.

About a month or so ago (fan again had been running, but apparently that was "normal", as it eventually stopped), after "disabling" current to the bathrooms (via the fuse box in the garage), I did take apart that switch, but did not see anything definitive there. I also removed the cover to the fan in the ceiling, but again saw nothing definitive there.

There is some small stains in the ceiling around 3 sides of that cover to the fan, but nothing serious (as far as I can tell). I also know that when they did the roof repairs, the contractors did need to "move" some vents, but I do not kn ow which ones.

I will send an EMail to the contractor about this, but can you folks provide any guidance, assistance, and/or insights as to why this is the case?

Thank You.

  • Can you post photos of the insides of the boxes for the fan and switch? – ThreePhaseEel Feb 22 '19 at 23:51

A light switch is a mechanical device with moving parts. They get used many thousand times over their lifespan. The switch could be bad. It is possible that in your case the failure is that the switch is staying closed, i.e., ON, when it is flipped OFF (the position in which it is supposed to be open).

Turn off the breaker to that particular switch. This should turn off the fan. (If the fan continues running, then either you have turned off the wrong breaker, or the workers wrongly connected the hot from another circuit to the fan so that it is being fed by two breakers. The contractor must correct this.)

Remove the two wires on the switch that controls the fan and move or bend them so the bare ends are out of the way. Neither of two ends should be hot (breaker is off) but if you have a non-contact tester make sure neither is hot.

With a multimeter in resistance mode touch the leads to the two screws on the switch from which you removed the wires. This is a check for "continuity", meaning if the switch is ON then you should read close to zero resistance (say micro ohms). If the switch is OFF, you should read very, very high resistance (mega ohms), meaning the switch is "open".

If you have low resistance when the switch is OFF, then the circuit is not being broken when you flip the switch OFF. Replacing the switch should fix the problem.

Replacing a switch is a relatively cheap way to begin troubleshooting your issue.

EDIT But consider the possibility that the fan has a moisture sensing switch in parallel with the manual wall switch. If you have this and either the sensor is faulty or a source of water is wetting the sensor, then this could keep the fan running even when the manual wall switch was OFF.

Moisture sensing fans do exist but one would have to know if they were supposed to be connected in parallel with a wall switch or in series with a wall switch, and could be both with two different wall switches but would probably be only in parallel.

  • Not clear whether you mean to wire nut the two wires together (in one wire nut) or you mean separate nuts on each wire. If the latter you could suggest that the OP then turns the breaker back on. If the fan runs with the wires thus not connected, then the switch is being bypassed. – Jim Stewart Feb 22 '19 at 20:29
  • Answer has been updated to reflect that issue. – Jerry_Contrary Feb 22 '19 at 21:07
  • OK, I will start by replacing that particular switch. Strange, though, that the "switch" just to the left of it, the one for the light in the bathroom, gets used a lot more than the one for the fan. Also, I understand that there are times when the fan should run continuously to keep the air fresh in our place. In those cases, the switch is off. With that scenario, is it as simple as replacing that particular switch? – Honestone Feb 22 '19 at 21:51
  • I have never heard of a simple switch for a bathroom exhaust fan being in parallel with some sort of auto sensing switch, but this may be possible. The way that would work is if either switch was ON, then the fan runs. – Jim Stewart Feb 22 '19 at 22:11
  • 1
    @JimStewart, if you look at a wall switch like this, it has three rockers and one of the rockers is only rated for 5 amps. That lower amp rocker is meant for a night light function OR and "auto sense" function. So it's essentially a contact closure that turns on an automatic function that's built into the fan rather than switching the fan directly. The other two rockers are used for a fan or light or heater. – JPhi1618 Feb 22 '19 at 22:28

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