Boiler
F12
The F12 error code on an Alpha boiler signals an ignition failure — the boiler has tried to light and failed, leaving you without heating or hot water. It can indicate a minor hiccup or a more serious gas or component fault, so it should not be ignored.
What does this error mean?
When your Alpha boiler displays F12, it means the burner failed to ignite during the startup sequence. The boiler’s control board detected no flame signal after attempting to fire, so it locked out as a safety measure. This lockout is intentional — it stops the boiler from repeatedly trying to ignite if something is genuinely wrong.
Est. repair cost
£150–£300 for electrode or sensor repair; £350–£500 for PCB replacement — all costs include Gas Safe labour
🔍 Likely causes
🛠️ Step-by-step fix
Check your gas supply first: confirm other gas appliances (hob, oven) are working. If they aren’t, call your gas supplier — the problem is upstream of your boiler.
Check your prepayment meter (if applicable) has sufficient credit and that the meter hasn’t tripped to emergency mode.
Press the reset button on your Alpha boiler (usually a flame symbol button or a dedicated reset button — check your model’s manual). Hold for 3 seconds and release, then wait 5 minutes for the boiler to attempt restart.
If the error clears, monitor the boiler through a full heating cycle. If F12 returns within a few hours, the fault is recurring and needs a Gas Safe engineer.
Do NOT attempt to inspect, clean, or adjust the ignition electrodes, gas valve, or any internal components yourself — this is illegal and dangerous without Gas Safe registration.
Turn the boiler off at the isolator switch and call a Gas Safe registered engineer if the reset does not clear the fault after one or two attempts.
📞 When to call a professional
Call a Gas Safe registered engineer if the F12 code returns after a reset, if your other gas appliances are working fine (ruling out a supply issue), or if you smell gas at any point — in which case call the National Gas Emergency line on 0800 111 999 immediately. Tell the engineer you have a persistent F12 ignition lockout fault on an Alpha boiler, and note whether it happens on heating calls, hot water calls, or both.
⚖️ Repair or replace?
Most F12 faults are repairable — electrode or flame sensor replacements typically cost £150–£300 including labour; a PCB replacement can reach £350–£500. If your Alpha boiler is over 10–12 years old and repairs exceed £400, replacing with a new A-rated combi (typically £1,800–£2,800 installed) is likely the better long-term investment. For boilers under 8 years old in otherwise good condition, repair is almost always the right call.