Oil Boiler Not Working — Common Causes & Fixes
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Post a job — we'll find you an engineer →Never attempt to repair the oil burner, fuel lines, or nozzle assembly yourself — oil heating work must be carried out by an OFTEC registered engineer. Oil spills and vapour are a fire hazard.
Oil boilers are reliable workhorses, but when they stop working, it can leave you without heating and hot water at a critical moment. The good news is that the cause is often something simple you can check yourself before calling an engineer out. Whether your boiler has locked out completely, won't fire up, or keeps shutting down unexpectedly, nine times out of ten the issue stems from fuel supply problems, electrical faults, or control settings rather than a serious breakdown. This guide walks you through the most common causes and the straightforward checks you can do safely yourself. If these steps don't get your heating back on, or if you notice signs of a burner fault, you'll need to contact an OFTEC registered engineer — and knowing what you've already checked will help them diagnose the problem more quickly.
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Most likely cause & what to check
Check the oil tank level first — running out of oil is the single most common reason an oil boiler stops working, and it is easy to overlook. Check the tank gauge or use a clean dipstick. If the tank is empty or very low (under 10%), order oil before calling an engineer — OFTEC engineers cannot bleed and restart a system without oil in the tank.
Check the boiler reset button — most oil boilers have a red or yellow reset button on the burner unit (the boxy unit at the front or bottom of the boiler). If the boiler has locked out on a fault, pressing this button once and waiting 30 seconds may restart it. Only reset once — if it locks out again, do not keep pressing reset as this can flood the combustion chamber with unburned oil.
Check the electrical supply — confirm the boiler isolator switch (usually near the boiler or at a fused spur) is on, and check the fuse or circuit breaker hasn't tripped. Oil boilers need electricity to run the burner motor, controls, and pump.
Check the thermostat and programmer — confirm the room thermostat is set above the current room temperature and the programmer is calling for heat. This sounds obvious but is frequently the cause.
Check the external oil line filter — many oil heating systems have a small filter (fire valve or line strainer) on the oil supply pipe between the tank and boiler. If this filter is blocked with sludge, the burner will run out of fuel and lock out. An OFTEC engineer can clean or replace this filter.
If the boiler fires briefly then cuts out, or makes unusual noises before locking out, there is likely a burner, nozzle, or ignition fault — call an OFTEC registered engineer. Oil burner servicing and repair requires specialist knowledge and equipment.
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Frequently asked questions
How long does it take to bleed an oil boiler after running out of fuel?
Bleeding an oil boiler system is a specialist job that only an OFTEC registered engineer can do safely and legally. The process typically takes 30 minutes to an hour, but it cannot be done until you've refilled the tank — the system needs oil present before bleeding can begin. Once the engineer has bled the system, your boiler should restart normally.
Why does my oil boiler keep locking out after I press the reset button?
Repeated lockouts usually indicate a fault with the burner, ignition electrode, or fuel supply line — not something you should keep resetting. Pressing reset more than once can flood the combustion chamber with unburned oil, making the problem worse. Stop pressing reset and call an OFTEC engineer to investigate the underlying cause.
Can a tripped electrics cause an oil boiler to stop working?
Yes — oil boilers rely entirely on electricity to power the burner motor, pump, and control circuits, so a tripped circuit breaker or blown fuse will prevent the boiler from firing. Check your fuse board or consumer unit and reset any tripped switches, then check that the boiler isolator switch is switched on. If the circuit keeps tripping, there may be an electrical fault and you should call a qualified electrician.
What does it mean if my oil boiler fires for a few seconds then shuts down?
Short firing cycles usually point to a problem with the burner, nozzle, or ignition system — these are OFTEC-only repairs. It can also indicate a blocked fuel line filter or air in the fuel line, but either way, you'll need an engineer to investigate safely. Do not keep trying to restart the boiler yourself.
Is it normal for an oil tank to have sediment or sludge in it?
Some sludge build-up is common in oil tanks over time, but excessive sludge can block the fuel line filter and prevent your boiler from running. If your system keeps cutting out and the tank appears full, a blocked external filter is likely — ask your OFTEC engineer to clean or replace it during their visit. Regular tank maintenance and keeping the filler cap sealed helps minimise contamination.