Why does my extractor fan run all the time?
A fan that will not stop is usually a humidity sensor set too sensitive for the room, or a timer doing exactly what it was set to do.
- Difficulty
- beginner
- Time
- 20 min
- Read
- 2 min
- Safety
- warning
Short answer
Work out which type you have. A humidity-controlled fan runs while it thinks the room is damp, so a low threshold or a genuinely humid house keeps it running. A timer fan runs for a set period after the light goes off. Both are adjustable, and adjustment usually means isolating the power and reaching small switches inside.
This is often reported as a fault when the fan is behaving exactly as designed. The useful step is establishing which control type is fitted, because a humidity sensor responding to a damp house and a timer set to its maximum are the same symptom with completely different causes.
Safety
Step by step
- Establish which control the fan has.A simple fan wired to the light switch, a timer model that overruns after the light goes off, or a humidity-controlled model that senses the room. The model number and its instructions will tell you.
- Rule out the simplest cause first.Some fans are wired to run continuously at a trickle rate by design, particularly in newer or well-sealed homes. That is a ventilation strategy, not a fault.
- For a humidity model, consider whether the room is genuinely humid.A fan running for long periods may be correct. Drying washing in the bathroom, long showers, or a house with a general moisture problem will all keep it running, and the fan is responding rather than malfunctioning.
- Check the humidity threshold setting.Most humidity fans have an adjustable trigger point. Set too sensitive, the fan responds to normal background humidity and rarely switches off. This is the usual adjustment.
- Check the overrun timer setting.Timer fans have a period adjustable from a few minutes to many. If it was left at maximum on installation, the fan runs far longer than anyone expects after every use.
- Isolate before removing any cover.The adjusters are usually inside the fan body, close to mains terminals. Isolate at the consumer unit, not just at the light switch, and confirm it is dead.
- Clean the sensor while you are there.A humidity sensor coated in dust reads inaccurately and can hold the fan on. Cleaning is part of servicing the fan, which GuideHQ covers separately.
- Consider whether the fan is failing to clear the room.A humidity fan that runs constantly may be trying and failing because the duct or terminal is restricted. In that case the running time is a symptom of a blockage, not of a setting.
Questions people ask
Is it expensive to leave running?
A domestic extractor fan uses very little power. The greater cost is the heated air it removes continuously in winter, which is a reason to set it sensibly rather than to disable it.
Can I just turn it off at the isolator?
You can, and then the bathroom has no ventilation. Condensation and mould follow, so it is worth adjusting the control rather than defeating it.