85 High

Keston 85 Fault Code

The Keston 85 fault code means: your boiler has stopped heating because a connected external safety device, such as a fire alarm or ventilation sensor, has signaled it to shut down.. It appears on 2 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: EXTERNAL INTERLOCK OFF
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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Keston models that show the 85 fault code

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

Source

Keston 85 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