BoilerFaultCodesJohnson Starley OVERHEAT LOCKOUT Fault Code
Also written as OVERHEATLOCKOUT — same fault.
The Johnson Starley OVERHEAT LOCKOUT fault code means: your boiler has shut itself down because it is getting too hot inside, usually because water is not flowing through your heating system properly.. It appears on 2 Johnson Starley models in our database.
Technical description: Flow/Return differential in excess of 30°C or circulation issues
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 OVERHEAT LOCKOUT fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Johnson Starley OVERHEAT LOCKOUT 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