BoilerFaultCodesGrant Off Fault Code
Also written as OFF — same fault.
The Grant Off fault code means: your boiler's burner has detected light when it should be dark inside, causing it to shut down for safety.. It appears on 6 Grant models in our database.
Technical description: Eliminate the extraneous light
What causes the Grant Off fault?
This fault occurs when the boiler's internal light sensor detects a flame or light source before the ignition process has even started. The most common reasons are a faulty sensor sending a false signal, a leaking fuel valve allowing a stray flame to persist, or light leaking into the burner housing through damaged seals.
DIY fix possible
Check that the burner cover and all casing panels are securely fitted and not letting in external light.Inspect the clear plastic viewing window for damage or missing seals.Press the reset button on the burner control box once all covers are tightened.
Find a Gas Safe engineer
Search the official register for a qualified engineer in your area.
Gas Safe Register →Grant models that show the Off fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Grant Off 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