Most exhaust fans replaced under complaint are not burnt out — they are dusty, loose, or running on a dead capacitor. A fan that is cleaned and checked on a schedule runs its rated airflow for years; one that is ignored loses 15–30% of it in a dusty workshop inside two seasons. This guide sets out what fails first, what to check each quarter, and the spares worth keeping on site.
Last updated: November 3, 2026
A fan is one of the few things on a building that can be judged before it fails. Dust on the blade, a shutter flap that no longer closes flat, a motor that hums a second before it spins — each one is visible or audible months before the unit stops. This page is the schedule we give to buyers who maintain their own installations, and the same list our own service team works from.
FAILURE ORDERAirflow loss and motor failure are usually the last two things to happen, not the first. In the warranty claims and spare-parts requests we handle, the order below is consistent across wall, panel and duct fans — and the first three items account for most of them.
| Order | What fails | How you notice it | Typical trigger | Repair |
|---|---|---|---|---|
| 1 | Run capacitor | Fan hums but does not spin; needs a nudge; spins slowly | Heat and age; a capacitor is a wear item with a shorter life than the motor | Replace capacitor — 10 minute job, lowest-cost repair on the whole fan |
| 2 | Blade fouling and imbalance | New vibration, rumble, or a fan that got noticeably quieter (because it is moving less air) | Dust, lint, grease or pollen building unevenly on one side of the blade | Clean and rebalance; check the shaft for play while the blade is off |
| 3 | Shutter mechanism | Flaps stay half open when off, rattle in wind, or stick when the fan starts | Dust in the rails, a bent flap pin, a stretched spring, or grease that has collected grit | Clean rails, straighten pins, replace the flap set; lubricate dry, never with grease |
| 4 | Bearings | Rumble that grows over weeks, or a grinding note at start-up | Dust ingestion and long idle periods; sealed bearings cannot be re-greased | Replace motor or bearing set — usually not economic on small panel fans |
| 5 | Motor winding | Trips the breaker, smells hot, or will not start at all | Almost always the consequence of a seized bearing or a blocked blade run for hours | Replace motor; find the cause first or the new one fails the same way |
Capacitor values differ by motor size: typically 1.0–2.0 µF on 100–150 mm fans, 2.0–3.5 µF on 200–250 mm and 4.0–8.0 µF on 300–450 mm. Always read the value printed on the old capacitor or the motor nameplate before ordering a replacement.
SCHEDULEThe interval is set by what the air carries, not by the fan. A bathroom fan in a house and a shutter fan on a welding bay are the same maintenance task at completely different frequencies.
| Installation | Clean blade and grille | Shutter / damper check | Electrical check | Full service |
|---|---|---|---|---|
| Home bathroom, kitchen, living space | Every 6 months | Every 12 months | Every 24 months | Every 24 months |
| Office, shop, clinic (light dust) | Every 3–6 months | Every 6 months | Every 12 months | Every 12 months |
| Workshop, warehouse, welding, woodworking | Every 1–3 months | Every 3 months | Every 6 months | Every 6–12 months |
| Commercial kitchen extraction | Every 1–3 months (grease) | Every month | Every 6 months | Every 6 months, plus duct clean per fire code |
| Coastal or high-humidity site | Every 3 months | Every 3 months | Every 6 months (insulation test) | Every 12 months |
| Seasonal / long idle | Before and after the season | Before the season | Before the season | Run 10 minutes every month while idle |
Intervals assume continuous daytime operation. For 24-hour duty, halve the cleaning interval. Where the fan runs against a filter, clean the filter more often than the fan — a loaded filter is what pushes the fan down its curve.
HOW TO CLEANThe single most common cleaning mistake is water in the motor. Everything else is recoverable; a wet winding is not. Isolate the fan at the breaker before any of the steps below, and do not rely on the wall switch alone.
Release the front grille, lift the blade off the shaft, wash the blade and grille in warm water with a mild detergent, and dry them fully. Wipe the housing with a damp cloth only — never hose the motor. Refit with the blade seated fully on the flat of the shaft and the grille screws firm, not over-tightened into plastic. Details per model on the KLT series page.
Clean the flap rails with a dry brush, then wipe with a cloth just damp with water. Do not lubricate the flaps with grease or oil: it holds dust and the flaps seize harder. If lubrication is needed, use a dry PTFE spray on the pins only. Check that every flap closes flat by hand and that no pin is bent — a single bent pin keeps the whole bank open and the fan then pulls air back through the gap when off. See shutter types.
Isolate, remove the access section or the fan body, and clean the impeller with a soft brush. Check the duct either side for lint and grease build-up — a clean impeller behind a blocked duct changes nothing. Replace the gasket if it is compressed or torn, and re-tape or re-clamp every joint you opened. Model data on the BXF duct fan page.
These carry a filter or a narrow grille; both load up. Vacuum the grille first, then wash the removable parts. Never run the fan with the filter removed for long: the dust simply moves into the impeller and the motor runs hotter. Fan noise rising over months is usually a loaded filter, not a failing motor.
These need a multimeter and, for the insulation test, a 500 V insulation tester. If nobody on site has them, an electrician can complete all four in under half an hour on a whole bank of fans.
For a site with more than about twenty fans, holding a small spares box turns a two-week wait into a same-day repair. These are the parts we ship most often, and they are available for any model we have supplied.
| Part | Why keep it | How to order it correctly |
|---|---|---|
| Run capacitor | First failure item, cheap, and the fan is unusable without it | Model plus the µF value printed on the old capacitor (or a photo of the nameplate) |
| Blade / impeller | Impact damage or a blade run out of balance after years of dust | Model, blade diameter, and a photo of the blade hub |
| Motor | Lets you repair a unit where the housing and shutter are still good | Model, voltage, frequency, and the date code from the label |
| Shutter flap set / spring | The most common non-electrical failure on wall fans | Model and frame size; flap sets are matched to the frame, not universal |
| Gasket and fixing kit | Every duct or wall re-fit needs one; a compressed gasket leaks air and water | Model and the mounting type (wall, window, duct) |
Send the model and the date code from the fan label when ordering spares — a photo of the label is enough. Parts are matched to the production batch, and the same model can carry different motors across years.
DECISIONThree rules cover almost every case:
Our standard warranty is 12 months on PP housing and blade models and 24 months on ABS models, against manufacturing defects from the date of shipment. Defective units are replaced or refunded after photo or video confirmation. It does not cover dust-blocked impellers, seized shutters, water ingress from hosing, or a motor destroyed by a failed capacitor that was left humming for weeks — which is exactly why the schedule above exists.
What each nominal size delivers, and how to measure the opening you actually have.
Room volume, air changes per hour, static pressure and how to pick the model.
Cut-out size, mounting height, wiring and the mistakes made on site.
Flap materials and mechanisms, and why a shutter jams when it is greased.
Send the model and the date code from the fan label (a photo is enough), a short description of what it is doing, and the quantity you need. We will confirm the part, the compatibility and the lead time — usually within one working day.