Video reference. The accompanying video is Ben Poulter's "Bathroom Extractor Fan Not Working Electrician Shows Easy Fault-Finding Fix" from the Toolbox Talks For Electricians YouTube channel. Ben is a UK-qualified electrician and his fault-finding videos cover real UK domestic jobs with UK wiring colours and regulations throughout.
1. Understand how your fan is wired
Before starting, it helps to know which of the three common wiring arrangements your fan uses, because this tells you where the power comes from and what controls it.
The most common arrangement in UK homes is a switched live feed from the bathroom light switch: the fan shares a switch connection with the light so that it comes on automatically when the light is turned on, often with a built-in timer that keeps it running for a few minutes after the light goes off. The second arrangement is a separate fused spur or timer switch, usually just outside the bathroom door. The third, common in newer builds, is a humidity sensor that triggers the fan independently of the light switch. Knowing your arrangement tells you whether to look first at the light switch wiring, the fused spur, or the fan's own sensor.
2. Check the consumer unit
Start at the consumer unit. Bathroom fans are almost always on the lighting circuit, typically protected by a 6A MCB. Scan the MCB row for any in the tripped position: handle midway between on and off, or slightly different in appearance to the rest. If one is tripped, reset it once and go back to test the fan.
If the MCB trips again immediately, there is a fault on the circuit that preventing further use safely. Do not keep resetting it. If all MCBs are in the on position, the supply to the fan is intact and the fault is local to the fan or its immediate wiring.
3. Check the local isolator or fused spur
Some fans are supplied through a fused connection unit (FCU) or isolator switch mounted outside the bathroom. These are easy to overlook. If there is a fused spur on the landing or hall wall near the bathroom, check that it is switched on. On an FCU with a replaceable cartridge fuse, unscrew the fuse carrier and check the fuse with a continuity tester or multimeter set to resistance: a good fuse reads near zero ohms; a blown fuse reads open circuit. A 3A fuse is standard for a bathroom fan. Replace it if blown and test the fan; if it blows again there is a short circuit in the fan or its wiring.
4. Remove the cover and check for obstructions
Isolate the supply, then remove the fan's front cover. Most clip-on covers release by squeezing the sides gently or pulling straight forward. Some have one small screw hidden under a cap. With the cover off you can see the impeller - the spinning fan blades - and often the motor assembly behind it.
Check the impeller for lint and dust buildup, particularly around the blade roots and the centre hub. A thick coating of fluff can add enough drag to stop the impeller turning, leaving the motor humming and overheating. Clean it with a soft brush or compressed air with the supply isolated. Then try spinning the impeller by hand: it should rotate smoothly with almost no resistance. If it feels stiff or grinds, there may be bearing wear or a physical obstruction between the impeller and the housing.
5. Check the wiring terminals
With the supply still isolated, look at the wiring connections inside the fan's terminal block. UK wiring colours since 2006 are brown (line), blue (neutral) and green-and-yellow (earth). Older wiring may be red (line) and black (neutral). Check that each wire is fully inserted into its terminal with no loose strands bridging across. Pull each wire gently - it should not come free.
A loose neutral is a particularly common cause of a fan that works intermittently or not at all. The symptom is that the fan sometimes starts, sometimes does not, with no obvious pattern. Retighten any loose connections and test. If the terminals look corroded or scorched, the connection has been arcing and the terminal block should be replaced - at which point the job is straightforward for a qualified electrician.
6. Listen for a hum without spinning
Restore the supply briefly and listen carefully. A fan that hums but the impeller does not move has almost certainly lost its run capacitor. The run capacitor is a small cylindrical component - usually 1 to 4 microfarads for a bathroom fan - that provides the phase difference the single-phase induction motor needs to generate starting torque. Without it, the motor field is balanced and the rotor has no reason to start turning.
Isolate the supply again. The capacitor is usually mounted on or near the motor body, with two wires connecting it. Its value in microfarads (µF) is printed on the side. A replacement capacitor matching this value costs £5 to £10 from an electrical factor or online. Discharge the old capacitor before removing it by briefly shorting its terminals through a resistor or a screwdriver with an insulated handle. Fit the replacement with the same polarity if it is a polarised type. If the fan then starts normally, the capacitor was the cause.
7. Decide: repair or replace
If the impeller is clean, the supply is present, the connections are tight and the capacitor is not the issue, the motor itself has likely reached the end of its life. Replacement motor assemblies exist for some fan models but are often nearly as expensive as a new fan. A straightforward axial bathroom fan costs £15 to £40 and fitting one on an existing circuit is within reach of a confident DIYer on most installations.
One constraint to be aware of: if the fan is located directly above the bath or shower tray (Zone 1) or within 60cm horizontally of it (Zone 2), BS 7671 has specific IP rating requirements for electrical equipment in those zones. A replacement fan must carry the appropriate IP rating for the zone. If you are unsure of the zone boundaries, or if the replacement requires extending or modifying the supply wiring, the work needs a qualified electrician and should be notified under Part P.
When to call us
Richard covers east Kent and is familiar with the bathroom fan wiring arrangements common in the area, from older red-and-black wiring through to humidity-controlled setups in new builds. If a fan is in a tricky location, the supply is tripping, or you want the replacement done correctly with a Part P certificate for insurance purposes, a single visit usually sorts it.
Bathroom fan fault in east Kent?
If the checks above haven't found the cause, or if the fan is in a bathroom zone and you need a Part P registered replacement, Richard can test and fix it.
Contact Richard