Boiler fan running but no ignition: what to check
Quick answer
If your boiler’s fan runs but it doesn’t ignite to produce heat or hot water, this often points to a fault somewhere in the ignition sequence — but the fan running at all tells you the boiler has power and is attempting to start. Note the fault code and whether it happens on heating, hot water, or both, and reset once only. If it keeps repeating the attempt and locking out, stop resetting and call an engineer.
Safety first
- Smell gas or suspect a leak: ventilate, leave the area, and call 0800 111 999.
- CO alarm sounding or anyone unwell: get fresh air and get urgent help.
- Do not remove boiler covers or attempt internal repairs.
- If the boiler attempts to light repeatedly, stop resetting and arrange a qualified check.
Full checklist: Safety guidance
What you may notice
- The fan runs, you hear clicking, then the boiler locks out — may point to an issue somewhere in the ignition or flame-sensing sequence, though the fault code will narrow this down.
- This only happens on hot water demand, or only on heating demand — can help identify which control path is affected.
- It’s happening during freezing weather — worth checking for a frozen condensate pipe, which is a common seasonal cause on many condensing boilers.
These are possible explanations, not a confirmed diagnosis. An engineer can confirm the exact cause on inspection.
Safe checks to make, in order
- Take a photo of the display/fault code/symbols.
- Check whether the issue happens on hot water demand, heating demand, or both.
- Check system pressure (sealed systems) and note the cold reading.
- If it’s freezing outside, check for a frozen condensate pipe (common on condensing boilers).
- Reset once only and observe: does it attempt ignition, then stop and show a code?
What you can do safely
- Take a photo of any fault code or warning symbol.
- Check whether the issue happens on heating, hot water, or both.
- Listen for the sequence: fan, clicks, then lockout.
- Reset once only if there are no danger signs and the manual allows it.
When to call a professional
- Any gas smell/CO alarm/unsafe signs.
- Repeated lockouts or recurring codes.
- You’re unsure how to interpret the code sequence.
What to tell the engineer
- Which of the checks above you carried out, and what you found at each step.
- Roughly when the problem started and whether it’s constant, intermittent, or linked to specific conditions (e.g. only when heating runs, only in cold weather).
- Any fault code, unusual noise, or visible sign you noticed.
- Whether the issue affects one fixture/radiator or several.
FAQs
Is it safe to keep pressing reset if the fan keeps running but nothing lights?
No — reset once and observe. If it repeats the same failed attempt, stop and call a Gas Safe engineer rather than continuing to reset, as repeated attempts don’t fix an underlying ignition fault.
What does it mean if I hear clicking before the lockout?
This is often the ignition attempting to spark. Combined with the fault code, this is useful information for an engineer, even though the exact cause needs proper diagnosis.
Could cold weather really stop my boiler from igniting?
Yes, particularly if the condensate pipe has frozen, which can trigger a lockout on many condensing boilers. See our guide on frozen condensate pipes for the safe way to check this.
Why does the fan need to run before ignition?
The fan proves that air can flow correctly through the boiler before it attempts to ignite, as part of its built-in safety sequence. This is a normal part of how the boiler starts up.
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