How much does it cost to fix Grant error code Slow flash?

Typical repair cost for the Grant Slow flash fault is £250-450 including labour.

Slow flash High

Grant Slow flash Fault Code

Q: What does the Grant Slow flash fault code mean?

Your boiler's electronic brain is experiencing a communication error, which is preventing it from firing up reliably.

Also written as SLOWFLASH — same fault.

The Grant Slow flash fault code means: your boiler's electronic brain is experiencing a communication error, which is preventing it from firing up reliably.. It appears on 5 Grant models in our database.

Technical description: Indicates a possible fault with the PCB (relay). (once every 2 seconds)

Typical repair cost £250-450 (including labour)

Engineer required

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

Find a Gas Safe engineer

Search the official register for a qualified engineer in your area.

Gas Safe Register →

Grant models that show the Slow flash fault code

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

Source

Grant 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 27 April 2026