25 High

Johnson Starley 25 Fault Code

The Johnson Starley 25 fault code means: your boiler's internal computer chips are failing to communicate correctly because of a software conflict or a hardware memory error.. It appears on 5 Johnson Starley 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: CRC error. Different software versions. Change ESYS.
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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Johnson Starley models that show the 25 fault code

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

Source

Johnson Starley 25 fault code information on this page is sourced and cross-checked against the official Johnson Starley service / installation manuals for each affected model.

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