Oil boiler locked out? How to reset it, and when to stop

An oil boiler locks out when the burner fails to light. You can reset it yourself, but Grant and Worcester Bosch both say to try only twice. Check the oil first: an empty tank is a common cause.

Checked against Grant's homeowner help and Worcester Bosch's oil boiler user instructions. Last reviewed October 2026. How we check

What to do, in order

Check there's oil in the tank. Running out is one of the causes of a lockout. Worcester Bosch, Grant
Check the boiler has power and the controls are asking for heat. The programmer should be on and the room thermostat turned up. On a Grant, no light on the on/off switch usually means no power or no signal from the controls. Worcester Bosch, Grant
Press the lockout reset button once. Where it is depends on the boiler: see below. Grant, Worcester Bosch
If nothing happens, wait 2 minutes and press it once more. Worcester Bosch
Stop there. If the lockout light is still on, don't keep resetting. Call an OFTEC registered engineer. Worcester Bosch, Grant

Where the reset buttons are

Grant

Lockout: the red lockout button on the front of the boiler. Grant says to try it only a couple of times.

Overheat: on the right-hand side of the control panel. Unscrew the black cap and press the button. If it clicks, it has reset. If it doesn't, the boiler may still be too hot, so let it cool first.

Grant

Worcester Bosch

Lockout: the burner reset button. On the Greenstar Danesmoor Utility it's on the burner control box behind the front panel; on the Danesmoor Utility ErP it's under the top panel.

Overheat: the ErP has separate boiler overheat and flue overheat resets. Press one if it's standing proud.

Worcester Bosch

Other models put the buttons in different places. Your user manual has a diagram.

Why oil boilers lock out

Grant lists these causes. We haven't found another manufacturer that lists them, so this is Grant's advice alone.

No oil, or a leak in the oil line to the boiler. Grant
Water in the tank, for example from a missing cover or condensation. Grant
Sludge from microbes growing where water meets oil in the tank. Grant
Rust from a corroding metal tank. Grant
For contaminated oil, Grant says to contact your oil supplier about cleaning the tank and flushing the oil lines. Grant

If you smell oil

Put out any naked flames. Worcester Bosch
Switch off the electricity to the boiler. Worcester Bosch
Turn off the oil supply to the boiler. Worcester Bosch
Open doors and windows. Worcester Bosch
Contact your installer or service engineer. Worcester Bosch

If oil is leaking from the tank, see what to do about a leaking oil tank.

Locked out in freezing weather?

Condensing oil boilers have a condensate pipe, like gas boilers. Grant says you can usually fix a frozen one yourself by thawing it with warm water. Grant Our frozen condensate pipe guide has the steps.

Call an OFTEC registered engineer if

The boiler is still locked out after two resets.
The overheat or lockout keeps coming back.
The boiler is hot but the heat isn't reaching the radiators. Grant says this can be a system fault or a faulty pump.
You can smell oil or see a leak.

Find an OFTEC registered technicianOpens OFTEC's official search.

Worcester Bosch says to have an oil boiler serviced at least once a year by an OFTEC registered engineer. OFTEC suggests having the tank checked at the same visit.

Common questions

How do I reset my oil boiler?

Press the lockout reset button. On Grant boilers it's the red button on the front. Worcester Bosch says to wait 2 minutes and press again if nothing happens. Both say to stop after two attempts and call an engineer.

How many times can I reset an oil boiler?

Twice. Worcester Bosch's manuals say to attempt only two burner resets, and Grant says to try its lockout button only a couple of times. Worcester's ErP manual adds: don't keep trying to start the boiler with the reset buttons.

Why does my oil boiler keep locking out?

Grant lists running out of oil, a leak in the oil line and contaminated oil as causes. Contamination can be water getting into the tank, sludge, or rust from a metal tank. Worcester Bosch says to check the oil level in the tank first.

Who services an oil boiler?

Worcester Bosch says to have an oil boiler serviced at least once a year by an OFTEC registered engineer. You can search for a registered technician on OFTEC's website.

What should I do if I smell oil?

Worcester Bosch says to put out any naked flames, switch off the electricity to the boiler, turn off the oil supply to the boiler, open doors and windows, and contact your installer or service engineer.

Sources

Last reviewed October 2026. Spotted something that doesn't match your manual? Email hello@boilercodes.co.uk and we'll check it. How we check