F.21 High
Your boiler has stopped working because it cannot light the flame or keep it burning properly.
Technical description: The pilot flame has failed.
Typical repair cost: £100-350 (including labour)
DIY fix possible
Check if your gas credit has run out or if other gas appliances in your home are workingPress and hold the reset button (the flame symbol with a cross) for 5 secondsWait 15 minutes and try resetting a second time if it fails again
Protect yourself from future repair bills
A boiler cover plan would cover faults like F.21 — no call-out fees, no surprises.
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Parts commonly replaced
- Ignition Electrode
- Flame Sensing Probe
- Gas Valve
- Ignition Lead
*Affiliate links — we may earn a commission at no extra cost to you.