Boiler
F11
The F11 error code on an Intergas boiler indicates a flame detection fault — the boiler is failing to detect a stable flame after ignition, which stops it from firing up safely. This is a moderately serious fault that will leave you without heating or hot water until it’s resolved.
What does this error mean?
F11 means your Intergas boiler attempted to ignite but either couldn’t establish a flame or lost the flame immediately after it started. The boiler’s ionisation sensor — the component responsible for confirming a flame is present — is not sending the expected signal back to the PCB. As a safety measure, the boiler locks out to prevent unburned gas from accumulating.
Est. repair cost
£150–£350 for a Gas Safe engineer call-out and parts (electrode or gas valve replacement); reset alone is free
🔍 Likely causes
🛠️ Step-by-step fix
Check your gas supply first: confirm other gas appliances (hob, gas fire) are working. If they’re not, contact your gas supplier — this is not a boiler fault.
Check your prepayment meter if applicable: a zero balance will cut gas to the boiler and cause F11.
Perform a boiler reset: locate the reset button on your Intergas boiler (usually a physical button or held via the display), hold it for 3–5 seconds, and wait for the boiler to attempt a restart. Consult your model’s manual for the exact reset procedure.
Wait and retry: if the reset clears the fault and the boiler fires, monitor it over the next few hours. A one-off lockout after a cold snap or power cut is not unusual.
If F11 returns repeatedly after resetting, stop here — do not attempt to open the boiler casing or interfere with the burner, electrodes, or gas valve. All further diagnosis and repair must be carried out by a Gas Safe registered engineer.
Book a Gas Safe engineer and describe the fault as an ‘F11 flame detection lockout’ — this helps them arrive prepared with the likely parts (ionisation electrode, ignition electrode, or gas valve).
📞 When to call a professional
Call a Gas Safe registered engineer if the F11 error returns after a reset, or if you’re unsure why it appeared. Any work beyond a reset — including cleaning electrodes, testing gas pressure, or replacing components — is legally required to be carried out by a qualified Gas Safe engineer on a gas appliance. Tell them you have a recurring F11 fault and that you suspect a flame detection or ignition issue.
⚖️ Repair or replace?
Most F11 repairs — replacing the ionisation electrode, ignition electrode, or gas valve — cost between £150 and £350 including labour, making repair the sensible choice for most boilers under 10 years old. If your Intergas boiler is over 12–15 years old and has had repeated faults, a replacement boiler (typically £2,000–£3,000 installed) may offer better long-term value. For newer Intergas boilers still within their 8–10 year warranty, contact Intergas directly before paying for any repairs.