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Damp, mould & condensation · Extractor fans

Why Does My Bathroom Extractor Fan Stay On After I Turn the Light Off?

For a bathroom extractor fan that continues running after the light has been switched off, either for a few minutes or apparently much longer.

By Home ManualReviewed 31 August 2026Safety level S2UK guidance
Quick answer

What this usually means

A bathroom extractor fan staying on after the light goes off is often completely normal. Many timer fans are designed to run on for roughly 5–30 minutes so they can remove moisture after you leave, while humidity-controlled or continuous-ventilation fans may run until humidity falls or may never switch fully off. It becomes a fault when a fan that used to stop now runs indefinitely, ignores its normal timer, behaves erratically, or will only stop at the isolator.

Likely causes

What may be causing this

1

The fan has a normal overrun timer

Clues: It starts with the light, then stops by itself after a consistent delay of several minutes.

What to do: This is intentional behaviour. Check the model instructions for the normal timer range before changing anything.

2

A humidity sensor is keeping the fan running

Clues: The fan runs longer after showers, stops sooner when the bathroom is dry, or starts/boosts without the light.

What to do: Humidity-controlled fans are designed to continue until moisture falls. Keep the grille clean and check the user-adjustable settings only if the manufacturer allows homeowner adjustment.

3

The fan is designed for continuous low-speed ventilation

Clues: It never fully stops but changes speed after a shower, light use or humidity increase.

What to do: Continuous operation can be part of the ventilation design. Do not switch it off permanently without understanding the system.

4

The timer, sensor or wiring has developed a fault

Clues: The fan used to stop normally but now runs indefinitely, the run-on time changes randomly, or it only stops when isolated.

What to do: An electrician should check the permanent live, switched live, timer/sensor controls and fan electronics.

Diagnose the pattern

How to check what is happening

Time how long the fan runs after the light goes off
It stops after roughly the same delay each time

A normal overrun timer is the most likely explanation.

Compare a dry bathroom with the period after a shower
The fan runs much longer when the room is humid

A humidistat or automatic moisture-control function is probably operating.

Look up the exact fan model without removing electrical covers
The manual describes timer, humidity or continuous modes

The behaviour may be a designed feature rather than a fault.

Recall whether the behaviour has changed
It used to stop but now runs continuously

A failed timer, sensor or control/wiring issue needs investigation.

DIY decision

Can you fix this yourself?

You can identify the fan model, time the overrun and observe whether humidity changes the run time. Those checks are enough to decide whether the behaviour is normal. Internal timer adjustments, wiring changes and fault diagnosis should be left to an electrician because timer and humidity fans may retain a permanent mains supply.

You'll usually need:
  • Phone timer
  • Phone camera for the visible model label
  • Manufacturer instructions
Step by step

What you can safely try

  1. 1

    Time the fan instead of guessing

    Switch the light off after normal use and record how long the fan continues. A repeatable 5–30 minute delay is common on timer models.

  2. 2

    Compare dry-room and post-shower behaviour

    If the fan runs longer after a steamy shower and less when the room is dry, a humidity sensor may be controlling it.

  3. 3

    Identify the fan model from visible markings

    Search the model number and read the operating instructions. Do not remove electrical covers just to find an internal label.

  4. 4

    Check whether it is a continuous-ventilation fan

    Some modern fans run continuously at low speed and boost when needed. Turning these off permanently can reduce the ventilation the home was designed to have.

  5. 5

    Get the controls checked if the behaviour has changed

    If a previously normal fan now runs indefinitely or behaves unpredictably, an electrician can test the timer, humidity control and switched/permanent live connections safely.

Stop conditions

Call an electrician if…

  • The fan, isolator or wiring smells hot or shows scorch marks.
  • The fan makes grinding noises, stalls or becomes unusually hot.
  • Any check would require removing an electrical cover or touching wiring.
  • The fan only stops by repeatedly operating or holding the light switch.
  • There is visible water entering the fan or duct.
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Evidence

Sources used for this guide

We prefer primary UK guidance, regulators and manufacturers for technical and safety-sensitive claims.

  1. VA100 Range Shutter & Timer FanVent-Axia
  2. Vent-Axia PureAir SenseVent-Axia
  3. Approved Document F (2026)GOV.UK

Last reviewed: 31 August 2026. Home Manual updates review dates only when the substance of a guide is checked or changed.

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