Boiler will not fire, red lockout light illuminated on the burner control box, no heating or hot water.

Safety first: Isolate electrical power to the boiler at the fused spur and turn off the oil supply valve before removing any covers. Allow the boiler to cool fully.

Basic checks (user level):

• Confirm there is oil in the tank and that all isolation valves on the oil line to the Grant burner are fully open.
• Press the reset/lockout button on the burner control box once only. If the boiler fires and runs normally, monitor it. If it locks out again, do not keep resetting.
• Check the boiler pressure gauge (on system) and top up via filling loop if system pressure is below manufacturer’s recommended level (typically around 1.0–1.5 bar when cold).

Technical checks (competent person only):

• Remove the burner and inspect the oil nozzle for blockage or damage; replace with the exact Grant-specified nozzle size and spray pattern.
• Inspect and clean the photocell (flame sensor); a dirty photocell can cause nuisance lockouts. Replace if the lens is crazed or discoloured.
• Check the ignition electrodes for correct gap and position relative to the nozzle as per Grant service manual; replace cracked or worn electrodes and HT leads.
• Bleed air from the oil pump using the bleed screw while running the burner (take fire precautions and use a suitable container).

If lockouts persist after these checks, the burner control box or oil pump may be faulty. In that case, contact a qualified Grant service engineer.