Six things to check, in order
- 01 Check the oil tank level, oil runs out more often than people expect.
- 02 Press the reset button on the burner. One press only, wait 30 seconds.
- 03 Check the fuel filter isn't clogged with water or sludge.
- 04 Check the fire valve, it should be fully open. Black TRV-style handle by the boiler.
- 05 Listen for the burner motor trying to fire. No hum = electrical fault.
- 06 Check the thermostat is calling for heat and batteries aren't dead.
The reset button, do this once, not repeatedly
Every oil burner has a red reset button (usually on the burner face or on a control box). If the boiler's locked out, one press of that button gives it another chance to fire.
Don't press it more than twice. If it locks out again, there's a fault, repeated resets pump raw oil into the combustion chamber, which is a fire risk and wastes oil you'll smell for weeks. Two presses, done.
Tank level, the easy one
Oil tanks in NI typically hold 1,000 or 1,350 litres. Watchman or gauge should show level. If it's running on sight-gauge, a cloudy or empty sight glass means empty. In winter a normal household burns 20–30 litres a day, so even a "three-quarter full" tank from October can be empty by February.
Order oil, top up, then press reset once. If the burner fires, you're done. If it fires then locks out again after a minute, there's air in the oil line, which is the next point.
Air in the fuel line (after running out)
If you've run out and just filled back up, air gets into the line and the burner can't pick up fuel. You need to bleed the line at the oil pump, usually a small brass nut on the pump housing. This is a 5-minute job for an engineer but not something you should try yourself unless you're confident with oil.
When itʼs engineer territory
If the six checks above don't fire the burner, you're into engineer territory. The most common deeper faults are:
- Photo cell dirty or failed, the sensor that detects flame. Easily replaced.
- Nozzle blocked or worn, standard service part. Replaced annually if you service.
- Pump pressure low, usually means the pump is tired.
- Control box failed, less common but not rare on older boilers.
A diagnostic call-out is £95 including the first hour. Most fixes (photocell, nozzle, minor parts) are completed on the day at a fixed price the installer agrees before starting.
Oil boiler not starting?
Every installer is OFTEC registered and installers service all major brands.
Warmflow, Grant, Worcester Heatslave, Firebird, Trianco. Same-day diagnostic across Belfast and 20 miles around.
Oil boiler servicing