How much does it cost to fix Grant error code Constant RED?

Typical repair cost for the Grant Constant RED fault is £120-250 including labour.

Constant RED High

Grant Constant RED Fault Code

Q: What does the Grant Constant RED fault code mean?

Your boiler has detected that the water inside it is getting too hot and has automatically paused to prevent overheating, but it should restart once it has cooled down sufficiently.

Also written as CONSTANTRED — same fault.

The Grant Constant RED fault code means: your boiler has detected that the water inside it is getting too hot and has automatically paused to prevent overheating, but it should restart once it has cooled down sufficiently.. It appears on 5 Grant models in our database.

Technical description: Thermal protection function may stop the pump temporarily. Occurs if the fluid temperature increases further beyond the blinking red threshold. Remains constant red until normal temperature conditions return.

Typical repair cost £120-250 (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 Constant RED fault code

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

Source

Grant Constant RED 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