Boiler
F18
The F18 error code on a Ferroli boiler indicates a fault with the ignition or flame detection circuit, meaning the boiler has failed to light or has lost its flame unexpectedly. It’s a fairly serious fault — your boiler will lock out and stop producing heat or hot water until the underlying cause is resolved.
What does this error mean?
F18 signals that the boiler’s control board has attempted to ignite the burner but either failed to detect a flame, or detected that the flame cut out shortly after lighting. The boiler’s safety system then locks out to prevent unburned gas from building up. This is a protective measure, not a glitch — something is genuinely preventing reliable combustion.
Est. repair cost
£80–£200 for a Gas Safe engineer call-out, diagnosis, and parts (electrodes, ignition lead, or gas valve replacement depending on cause)
🔍 Likely causes
🛠️ Step-by-step fix
Step 1 – Check your gas supply: Turn on a gas hob or other gas appliance to confirm gas is reaching your home. If nothing is working, contact your gas supplier immediately — do not attempt to reset the boiler.
Step 2 – Reset the boiler: Press and hold the reset button (usually marked with a flame or ‘R’ symbol) for 3–5 seconds, then release. Wait up to 2 minutes to see if the boiler fires up successfully.
Step 3 – Repeat the reset once more if the first attempt fails. Ferroli recommends no more than two consecutive reset attempts — repeated lockouts point to a real fault that needs investigation.
Step 4 – Check the boiler pressure gauge: Low system pressure (below 1 bar) can contribute to ignition problems. If the needle is below 1 bar, top up via the filling loop following your boiler’s manual instructions.
Step 5 – If the F18 returns after reset and the pressure is correct, stop here. This fault requires a Gas Safe registered engineer — do not open the boiler casing or attempt to inspect the electrodes or gas valve yourself.
📞 When to call a professional
Call a Gas Safe registered engineer if the F18 error returns after two reset attempts, or immediately if you smell gas at any point. Tell the engineer you have an F18 lockout on a Ferroli boiler and that you suspect an ignition or flame detection fault — this helps them bring the right parts. Do not use the boiler until it has been inspected.
⚖️ Repair or replace?
Most F18 faults are repairable at a reasonable cost — ignition electrodes and leads are inexpensive parts and labour is typically under two hours. If your Ferroli boiler is over 10–12 years old and this is one of several recent faults, the repair bill may approach or exceed 20–25% of a new boiler’s cost, at which point replacement is worth considering. A new A-rated combi boiler installed typically costs £1,800–£2,800 in the UK.