How much does it cost to fix Johnson Starley error code Error 04?

Typical repair cost for the Johnson Starley Error 04 fault is £60-120 including labour.

Error 04 High

Johnson Starley Error 04 Fault Code

Q: What does the Johnson Starley Error 04 fault code mean?

Your boiler has stopped working because the water pressure inside the system has dropped too low for it to operate safely.

Q: Can I fix Johnson Starley fault code Error 04 myself?

Locate the external filling loop, which is usually a silver flexible hose with two small valves.

Also written as ERROR04 — same fault.

The Johnson Starley Error 04 fault code means: your boiler has stopped working because the water pressure inside the system has dropped too low for it to operate safely.. It appears on 1 Johnson Starley model in our database.

Technical description: Critically low water pressure (<0.3bar).

Typical repair cost £60-120 (including labour)

DIY fix possible

Locate the external filling loop, which is usually a silver flexible hose with two small valves.Slowly open both valves to allow water into the system while watching the pressure gauge.Close both valves tightly once the gauge reaches between 1.0 and 1.5 bar.

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Johnson Starley models that show the Error 04 fault code

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

Warmcair DW Repair: £60-120

Source

Johnson Starley Error 04 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