Home › Heating › Boiler Fan Running Constantly

BOILER SYMPTOMS & WARNINGS

Boiler Fan Running Constantly

A boiler fan may continue running during normal purge or overrun, but constant operation can indicate a control-board, air-pressure or fan-sensing fault.

!
!

Use only safe external checks and do not open the boiler casing

Boilers contain gas, combustion components, mains electricity and hot pressurised water. Repeated lockout, burning smells, leaking or severe noise requires professional inspection.

MOST LIKELY CAUSES

Start with these

Normal purge or overrun The fan may run briefly before or after firing.
Stuck relay or control fault The fan may remain energised.
Air-pressure sensing fault The boiler may keep trying to prove airflow.
Repeated failed ignition The fan may cycle during restart attempts.
◫ Symptom variations Match the exact noise, lockout or display pattern. ⌄
  • Fan runs with burner off
  • Fan continues long after demand ends
  • Boiler does not ignite
  • Fault code appears
  • Fan restarts repeatedly
✓ Quick checks Safe checks before calling an engineer. ⌄
  1. Record the exact fault code.
  2. Check system pressure.
  3. Confirm thermostat and programmer demand.
  4. Check visible condensate and external pipework.
  5. Reset once only if the manual permits.
1 Step 1 — Check whether the boiler is still in a normal cycle Use only safe external checks and follow the boiler manufacturer instructions. ⌄

Allow several minutes after demand ends.

2 Step 2 — Check the display and fault code Use only safe external checks and follow the boiler manufacturer instructions. ⌄

Record any message before resetting.

3 Step 3 — Turn off demand at the thermostat Use only safe external checks and follow the boiler manufacturer instructions. ⌄

See whether the fan eventually stops.

⌁ Common causes explained Why boiler symptoms and warnings develop. ⌄

A boiler fan may continue running during normal purge or overrun, but constant operation can indicate a control-board, air-pressure or fan-sensing fault.

⌘ Advanced diagnostics Heating-engineer checks and repair work. ⌄
  • Test fan relay output.
  • Check air-pressure switch or sensor.
  • Inspect fan feedback signal.
  • Verify ignition sequence.
  • Check control-board logic.
▣ Parts that may need replacing Common components linked to this fault. ⌄
  • Boiler fan
  • Air-pressure switch
  • Pressure sensor
  • Control board
  • Wiring harness
! When to call a heating engineer Conditions that should end basic troubleshooting. ⌄
  • The boiler repeatedly locks out.
  • There is a gas or burning smell.
  • The boiler bangs, overheats or leaks.
  • The casing would need to be opened.
  • A fuse or breaker trips repeatedly.
? Frequently asked questions Common boiler warning questions. ⌄

How many times should I reset a boiler?

Once, following the manufacturer instructions. Repeated reset attempts can hide a serious fault.

Can I open the boiler casing?

No. Combustion and gas-related parts must be handled by a properly qualified engineer.