How much does it cost to fix Grant error code Lock-out (light on)?

Typical repair cost for the Grant Lock-out (light on) fault is £120-250 including labour.

Lock-out (light on) High

Grant Lock-out (light on) Fault Code

Q: What does the Grant Lock-out (light on) fault code mean?

Your boiler has stopped itself from running as a safety precaution because the fuel failed to ignite properly.

Also written as LOCKOUTLIGHTON — same fault.

The Grant Lock-out (light on) fault code means: your boiler has stopped itself from running as a safety precaution because the fuel failed to ignite properly.. It appears on 5 Grant models in our database.

Technical description: Burner not starting - fuel and electricity supplies present. Press the reset button on the burner control box.

Typical repair cost £120-250 (including labour)

DIY fix possible

Check your external oil tank has enough fuel and the isolation valve is fully openLocate the red reset button on the burner casing or control boxPress and hold the reset button for 3 seconds then release to attempt a restart

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Grant models that show the Lock-out (light on) fault code

Click a model for the full fault code list and model-specific repair notes.

Source

Grant Lock-out (light on) fault code information on this page is sourced and cross-checked against the official Grant service / installation manuals for each affected model.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026