Boiler fan running constantly, even when heating is off
A fan is expected to run only during ignition and while the burner is firing, plus a brief post-purge afterwards. A fan that carries on well beyond that, or runs with no call for heat at all, is behaving outside its normal control logic.
What is actually going on with a boiler fan running constantly
A relay or control board fault that fails to switch the fan off cleanly is a common cause, alongside a fan motor with a failing capacitor that runs erratically rather than stopping properly. On some appliances a stuck pressure switch keeps signalling that airflow is still required even once the burn cycle has ended, which the control logic interprets as needing the fan to keep running. Continuous unnecessary running shortens fan bearing life and wastes a small but real amount of electricity.
Key points on a boiler fan running constantly
- Normal fan running covers ignition, the burn and a brief post-purge only
- A relay or control fault can fail to switch the fan off cleanly
- A failing capacitor makes fan motors run erratically rather than stop
- A stuck pressure switch can falsely signal ongoing airflow demand
- Continuous running shortens bearing life and wastes electricity
Relevant registrations
- Gas Safe registered for domestic gas boiler work
- OFTEC registered for oil boiler work
- Worcester Bosch Accredited Installer
Questions we get asked
- Is it safe to keep using the boiler like this?
- It will usually still heat the home, but the underlying control fault should be checked before it develops further.
- Could this be a wiring issue rather than the fan itself?
- Yes — relay and control wiring faults are checked alongside the fan and its capacitor.
Where we deal with this
Related help pages
- Winter oil faultOil boiler will not start in cold weather: waxing, water and filters
- Glow-worm fault codeGlow-worm F22: low water pressure on an Ultracom or Betacom
- Zero pressure diagnosisBoiler pressure reading zero: is it a leak or a dead gauge
- Vaillant fault codeVaillant F22: low water content and what it is really telling you
- Vokera rangeVokera Easi-Heat: an older combi still common in servicing calls
- Efficiency controlsLoad compensation: how a modern boiler reads your room temperature
Services that cover this
Straight answers on a boiler fan running constantly
The honest position: A fan that will not stop is a control logic symptom as much as a mechanical one — both are checked together.
Call Jamie Crawford Heating on 07516 118198 during the published weekday opening hours.
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