Why Does My Extractor Fan Not Work Properly?

A bathroom extractor fan that isn't working properly is most often caused by a blocked or restricted duct, a worn-out motor, or a fan that was undersized for the room from the start. Left unfixed, poor extraction leads to condensation, mould and, over time, damage to decoration and even structure.

Common causes and fixes

• Dust and grease build-up on the fan blades or grille reduces airflow significantly over time. This is the simplest cause to fix — isolate the electrics, remove the cover, and clean the blades and grille thoroughly. Many fans benefit from this every 6-12 months.
• Blocked or crushed ducting — if the duct run to outside has been squashed, has too many tight bends, or has become blocked with debris or a bird's nest at the external vent, even a healthy fan won't clear air effectively. Worth checking the external vent isn't obstructed.
• Worn motor bearings cause a noisy, weak, or intermittently working fan — usually a sign the fan itself needs replacing rather than repairing, since fan motors aren't generally cost-effective to repair individually.
• Fan undersized for the room — UK Building Regulations (Part F, ventilation) set minimum extraction rates for bathrooms, and a fan that technically works but was undersized for the room will never clear steam effectively no matter how well maintained it is.
• No or a poor humidity/timer setting — many fans run on a timer or humidity sensor; if this is set too short, the fan switches off before steam has actually cleared.

Types of bathroom extractor fan

There are two main types installed in UK bathrooms. Axial fans sit directly in the wall or ceiling and are the simplest, cheapest option, but they're less powerful over longer duct runs. Centrifugal (inline) fans are more powerful and quieter in the room itself since the noisy motor unit can be positioned in the loft or a cupboard away from the bathroom, with only ducting and a grille in the room — a better choice where the extraction point is more than a metre or so from the fan unit, or where noise is a particular concern. If your current fan struggles despite a clear duct and clean blades, it may simply be the wrong type for how far the air needs to travel to get outside.

It's also worth checking the fan's humidity sensor calibration if it has one — many humidity-sensing fans have a small adjustable dial inside the housing that sets the trigger threshold. If it's set too high, the fan won't switch on until the room is already very steamy; set correctly, it should activate close to when a shower starts and run on for a few minutes after to fully clear the air.

How to check if your extraction rate is adequate

A simple check: hold a piece of tissue paper near the grille while the fan is running — it should be pulled firmly against the grille, not just flutter weakly. If it barely moves, either the fan is failing or was undersized to begin with. UK regulations generally expect a bathroom extractor to achieve at least 15 litres per second of extraction (higher for an ensuite with a shower only and no window) — a specification worth checking against your fan's rated output if you suspect it's underperforming.

When to call a professional

Cleaning the fan and checking the external vent are safe DIY tasks once the electrics are isolated. Replacing the fan unit itself involves electrical work in a bathroom's regulated zones, which falls under Part P and should be done by a qualified electrician — this is not a place to cut corners, both for safety and because it needs proper certification.

Why this matters beyond comfort

Poor bathroom ventilation is one of the most common causes of mould and damp in UK homes — if you're seeing black spots on the ceiling or around the window, it's worth reading our guide on why bathrooms grow mould alongside fixing the extraction itself, since the two problems usually go together.

Common mistakes

• Never cleaning the fan — a fan that hasn't been cleaned in years is often not actually broken, just clogged.
• Blocking or covering the grille with paint or decorating materials, which restricts airflow even when the fan itself is fine.
• Assuming a working fan is an adequate fan — a fan can run without fault and still be too small for the room and shower output.

If you're planning a new ensuite bathroom without an external wall, factoring in a properly ducted extractor fan run is essential — a fan with nowhere direct to vent to outside is one of the most common ventilation mistakes in ensuite conversions.