BURNER Slow flash High

Grant BURNER Slow flash Fault Code

Also written as BURNERSLOWFLASH — same fault.

The Grant BURNER Slow flash fault code means: your boiler's electronic control brain is experiencing a malfunction and can no longer safely manage the burner operation.. It appears on 3 Grant models in our database.

Call an engineer soon

Book a Gas Safe engineer within 24 to 48 hours. Your boiler may be unsafe or could break down completely if left.

Technical description: Indicates a possible fault with the PCB (relay). Replace PCB.
Typical repair cost £250-450 (including labour)

Engineer required

This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

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Grant models that show the BURNER Slow flash fault code

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

Source

Grant BURNER Slow flash 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 7 July 2026