BoilerFaultCodesJohnson Starley b25 Fault Code
Also written as B25 — same fault.
The Johnson Starley b25 fault code means: your boiler’s internal computer chip has encountered an error and is unable to communicate properly with the rest of the unit.. It appears on 4 Johnson Starley models in our database.
Technical description: Internal control fault
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
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Gas Safe Register →Johnson Starley models that show the b25 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Johnson Starley b25 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 27 April 2026