Oil Boiler Flame Failure Lockout
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Post a job — we'll find you an engineer →Only reset an oil boiler once or twice. If it continues to lock out, repeated resets with unburned oil present is a fire risk. Call an OFTEC engineer.
Flame failure lockout means the oil boiler attempted to light, may have achieved ignition briefly, but the flame sensor (photocell or cad cell) did not detect a stable flame. The boiler shut off as a safety measure. This is one of the most common oil boiler faults and has several potential causes.
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Most likely cause & what to check
First, check the oil tank level — if below 10–15%, the burner may be drawing air rather than oil, causing intermittent flame failures. Order a delivery and wait 30 minutes after it arrives before attempting to restart.
Try resetting the boiler — press the red reset button on the burner (Riello, Danfoss, or similar). Hold for 3 seconds and release. The boiler should attempt ignition.
If the boiler ignites briefly then shuts off (rather than not igniting at all), the photocell (flame sensor) is likely dirty. The photocell is a small glass-ended sensor that watches the flame — if it is covered in soot, it cannot see the flame and signals lockout. An OFTEC engineer can clean or replace this cheaply as part of a service (£80–160).
If the boiler does not ignite at all, check the ignition electrodes — these fire a spark to light the oil spray. Worn or incorrectly gapped electrodes will not produce a reliable spark. Electrode replacement is an OFTEC engineer job.
Check the oil supply filter (usually a small glass bowl on the oil supply pipe near the boiler) for water contamination or sediment — water in the oil supply is a common cause of flame failures, particularly after a fresh delivery disturbs tank sediment.
The burner nozzle atomises the oil into a fine mist for ignition — a blocked or worn nozzle prevents correct combustion. Nozzle replacement is included in most OFTEC annual services and costs £30–80 for the part.
An OFTEC registered engineer must carry out any repairs to oil burner components — this is a legal requirement for oil-fired appliances. Check the OFTEC register at oftec.org.
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