How much does it cost to fix Johnson Starley error code 40?

Typical repair cost for the Johnson Starley 40 fault is £80-220 including labour.

40 Medium

Johnson Starley 40 Fault Code

Q: What does the Johnson Starley 40 fault code mean?

Your boiler has detected that there is too much water pressure in the system, which can cause the safety valve to leak or damage internal components.

The Johnson Starley 40 fault code means: your boiler has detected that there is too much water pressure in the system, which can cause the safety valve to leak or damage internal components.. It appears on 6 Johnson Starley models in our database.

Technical description: High system water pressure

Typical repair cost £80-220 (including labour)

DIY fix possible

Check that the filling loop valves are fully closed and not letting in waterBleed water from a radiator using a bleed key to reduce the system pressureMonitor the pressure gauge to ensure it returns to between 1.0 and 1.5 barReset the boiler once the pressure is within the normal operating range

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Johnson Starley models that show the 40 fault code

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

Source

Johnson Starley 40 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