Johnson & Starley F47 Fault Code: Causes, Fixes & Repair Costs
What does the Johnson & Starley F47 fault code mean?
F47 on a Johnson & Starley unit means the water pressure sensor is not connected — the control board can see no signal at all from the sensor that reports sealed-system pressure on the water-carrying models. This differs from F37/F40 (pressure genuinely low or high): here the board has lost the sensor itself. Without a pressure reading the controller cannot protect the water side against running dry or over-pressurised, so it shuts that side down. The causes are exactly what the name suggests: an unplugged or corroded connector, a broken lead between sensor and board, a failed sensor presenting as open-circuit, or — rarely — the board input.
General guidance only — not a substitute for professional advice, and not certified by a Gas Safe engineer. Always have your specific appliance assessed by a qualified professional. Any gas work must be carried out by a Gas Safe registered engineer. If you smell gas or suspect carbon monoxide, leave the property and call the National Gas Emergency line on 0800 111 999.
Common causes
- Connector dislodged or corroded Common
The sensor's plug works loose with vibration or corrodes in the damp lower regions of the case — the most common and cheapest finding, especially after recent service work.
- Failed pressure sensor Common
The transducer fails open-circuit, indistinguishable from 'not connected' as far as the board is concerned; replaced once the wiring is proven.
- Broken loom or board input Sometimes
A damaged lead or, rarely, the board's input circuit; diagnosed by checking the signal at each end.
How to fix it
- Reset once and observe DIY safe
Use the reset control (or switch off at the fused spur for 30 seconds and back on) a single time. If the code returns, stop resetting and book a Gas Safe registered engineer.
- Mention any recent service or repair work DIY safe
If the unit was recently worked on, a connector left off is the likely story — telling the engineer saves diagnostic time.
- Have a Gas Safe registered engineer complete the documented checks Gas Safe engineer
The engineer will check the pressure sensor's connector and lead, reseat or repair as found, and test the sensor's output — replacing it if open-circuit. They should verify the displayed pressure matches a gauge reading before handing back.
Parts you may need
- Water pressure sensor · from £40
The exact spare depends on your boiler's GC number (on the data badge). Check this against the part before buying.
Typical repair cost
Expect to pay roughly £90–£250, depending on the underlying cause.
Frequently asked questions
What does F47 mean on my Johnson & Starley?
The board can see no signal from the water pressure sensor — unplugged, broken lead, or the sensor failed open-circuit. The water side shuts down because it cannot be protected without a pressure reading. Usually a quick fix: reseat the connector or fit a new sensor.
Is this the same as low pressure?
No — F37 means the sensor reports pressure genuinely low; F47 means the sensor is silent altogether. Do not add water in response to F47: the system pressure may be perfectly fine, and the fault is electrical.
What will it cost?
Among the cheaper faults — a reseated connector may cost only the visit, and the sensor itself is around £40. Expect roughly £90–£250 all-in depending on findings and region.