Fan Fault on a Boiler: Why the Fan Won't Run
A fan fault on a boiler means the controls asked the fan to start but it did not reach speed, or the air pressure switch never proved airflow, so the boiler locks out for safety before it lights — common causes are a seized fan bearing, a failed fan motor, a wiring fault or a blocked flue.
A fan fault on a boiler means the controls asked the fan to start but it did not reach speed, or the air pressure switch never proved airflow, so the boiler locks out for safety before it lights — common causes are a seized fan bearing, a failed fan motor, a wiring fault or a blocked flue. The boiler tries to start, you hear a click, then it stops without the usual whoosh of the fan spinning up.
What is actually going on
The boiler tries to start, you hear a click, then it stops without the usual whoosh of the fan spinning up.
The realistic causes, in order
A seized fan bearing, common where a boiler sits in a dusty loft or garage and has had years of intermittent duty A failed fan capacitor or open winding, so the fan draws current but never reaches the speed the PCB expects A PCB or wiring fault that never delivers the run signal, often at a corroded connector behind the case
What we test on site
Fan speed feedback against the manufacturer's expected RPM range for that model Supply voltage at the fan plug while the boiler attempts a start sequence The wiring loom and connector block for heat damage or green corrosion
Noises that point to the fan
A fan that hums without spinning, whirrs then stops, or grinds as it starts is often on its way out. A fan that runs normally but still triggers a fault suggests the air pressure switch, its tubing or the flue instead. Because the fan sits inside the sealed room-sealed case, all of these checks are for a Gas Safe engineer.
Worth checking today if you have a boiler fan that won't run
- Listen at start-up — silence where you'd normally hear the fan is the useful clue to report
- Note the fault code on the display before switching the boiler off and on
- A boiler will not run its ignition sequence without proven fan operation, because the fan is what proves the flue can clear combustion products. Never bypass or override it.
Who does the work
- Gas Safe registered engineers — registration 554328
- Worcester Bosch accredited installer
- John The Plumb Ltd, company registration 10026483
Get a boiler fan that won't run diagnosed properly
Fans are stock items for common models, so this is usually a same-visit repair once the diagnosis is confirmed.
Questions we get asked
What causes a boiler fan that won't run on a gas boiler?
A seized fan bearing, common where a boiler sits in a dusty loft or garage and has had years of intermittent duty
What normally puts a boiler fan that won't run right?
Fans are stock items for common models, so this is usually a same-visit repair once the diagnosis is confirmed.
Should I switch anything off because of a boiler fan that won't run?
A boiler will not run its ignition sequence without proven fan operation, because the fan is what proves the flue can clear combustion products. Never bypass or override it.
Is it safe to keep resetting a boiler with a fan fault?
One reset is fine. If the fan fault returns, leave it off and book an engineer — the fan moves combustion gases out, so it should not be forced to run.