Before you start
Oil boiler lockout codes vary slightly by brand (Warmflow, Grant, Firebird, Worcester Heatslave all use slightly different systems). The most common are listed below. If yours isn't here, check the boiler's user manual, every modern oil boiler has one printed inside the casing.
Don't reset more than twice. Every reset dumps unburnt oil into the combustion chamber. After the second failed reset, stop and call an engineer.
Common codes at a glance
- F1 Press reset, check tank, call engineer if repeated.
- Lockout, most common oil boiler fault. Burner tried to fire and failed. Reset once; if it locks again it's a fuel, photocell or ignition issue.
- F2 Check pump running, radiators hot. Could be a failed pump or stuck valve.
- Overheat, boiler got too hot (often because flow is blocked).
- F3 Look for bird nest, debris at flue terminal. Don't run boiler until cleared.
- Flue fault, pressure sensor detecting blocked flue.
- F4 Clean the photocell, check combustion chamber. Engineer visit likely.
- No flame signal, burner is firing but photocell isn't seeing the flame.
- L1 / L2 Reset once; persistent lockout needs engineer.
- Warmflow lockout, similar to F1 but on Warmflow-specific controls.
- E1 / E2 Power-cycle the boiler. If persistent, engineer.
- Firebird-specific electrical or ignition fault.
F1 lockout, by far the most common
Seven out of ten oil boiler calls the network takes are an F1 or equivalent lockout. The cause, in rough order:
- Out of oil, check the tank first.
- Air in the fuel line, usually after filling from empty.
- Blocked fuel filter, service part, due annually.
- Failed photocell, dirty or degraded, usually after 10+ years.
- Worn nozzle, service part, due annually.
- Ignition electrode faulty, less common but it does come up.
An annual service replaces nozzles, photocells and filters as standard, which prevents most of the above. If you've skipped the last service or two, a service is the fix for 80% of lockouts.
Overheat (F2 and equivalents)
An overheat lockout means the boiler reached excessive temperature and the safety stat cut it off. Nearly always a flow problem: pump failed, air-locked pipework, or a stuck motorised valve. Safe to leave off overnight, but don't keep resetting it until the underlying flow issue is sorted.
Flue fault (F3)
Blocked flue, pressure-sensor fault or (more dangerous) a back-draft issue. If you smell combustion fumes indoors, turn the boiler off and open windows. This one isn't DIY territory, message us and an installer will come out the same day.
When itʼs engineer territory
If a reset doesn't clear the lockout on the first try, that's engineer territory. Send a quote request. Same-day diagnostic £95 plus whatever the fix costs (agreed before the work starts).
Oil boiler locked out?
OFTEC registered, same-day response.
Warmflow, Grant, Firebird, Worcester Heatslave, installers service every major NI oil brand.
See oil boiler servicing