F7 High

Keston F7 Fault Code

The Keston F7 fault code means: your boiler has stopped working because the electrical supply from the grid or your home's wiring has dropped below the level required for the unit to run safely.. It appears on 3 Keston 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: LOW MAINS VOLTAGE - CONTACT ELECTRICITY PROVIDER
Typical repair cost £100-350 (including labour)

Engineer required

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

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Keston models that show the F7 fault code

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

Source

Keston F7 fault code information on this page is sourced and cross-checked against the official Keston service / installation manuals for each affected model.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 7 July 2026