Boiler
F12
The F12 error code on an Intergas boiler indicates a flame detection or ignition failure — specifically, the boiler is attempting to ignite but cannot detect a stable flame. This is a moderate-to-serious fault that will leave you without heating or hot water until it’s resolved.
What does this error mean?
F12 means your Intergas boiler has tried to light its burner but the ionisation sensor — the component that confirms a flame is present — hasn’t detected one. The boiler makes a set number of ignition attempts, fails to establish a flame, and locks out as a safety measure. This lockout protects your home from unburned gas accumulating, so it should never be bypassed.
Est. repair cost
£80–£150 for a call-out and electrode replacement; £200–£400 for a gas valve replacement; PCB replacement £250–£500 including parts and labour
🔍 Likely causes
🛠️ Step-by-step fix
Check your gas supply first: make sure other gas appliances (hob, oven) are working. If not, contact your gas supplier — there may be a supply interruption in your area.
If you have a prepayment meter, check you have sufficient credit and top up if needed.
Inspect the condensate pipe (the white plastic pipe, usually running to an outside drain or internal waste pipe). If it’s frozen or blocked, carefully thaw it with warm (not boiling) water and clear any blockage — this is safe DIY.
Once you’ve addressed any of the above, reset your Intergas boiler: press and hold the reset button (usually marked with a flame or ‘R’ symbol) for 3–5 seconds, then wait for the boiler to attempt restart.
If the boiler fires up and runs normally, monitor it over the next 24 hours. If F12 returns immediately or within a short time, the fault is internal and you must stop here.
Do NOT attempt to inspect or clean the electrodes, gas valve, or PCB yourself — these tasks require a Gas Safe registered engineer by law.
📞 When to call a professional
If resetting the boiler doesn’t clear the F12 code, or if the fault returns after a successful reset, call a Gas Safe registered engineer immediately — do not attempt further DIY on any internal gas components. Tell the engineer: ‘My Intergas boiler is showing an F12 lockout fault — I suspect an ignition or flame detection issue.’ They will test the ionisation and ignition electrodes, gas valve, and PCB to pinpoint the fault.
⚖️ Repair or replace?
For an Intergas boiler under 10 years old, repair is almost always the right call — Intergas boilers have a strong reliability record and parts are readily available. If your boiler is over 12–15 years old and facing a PCB or gas valve replacement, a new boiler (£2,000–£3,500 installed) may offer better long-term value. An electrode replacement or gas valve service is typically well within economical repair territory.