Error S.54

Safety first

1) If you smell gas, leave the property immediately and call the emergency gas number. Do not try to fix anything yourself. If there is any electrical or flame-related fault, switch the boiler off at the mains and isolate the gas supply only if you are trained to do so.

2) Do not remove boiler covers or attempt internal electrical/gas repairs. Those actions are for a Gas Safe registered engineer only.

Initial homeowner checks (safe, simple steps)

1) Note the display: write down the exact code(s) shown (S.54 and any accompanying F‑codes) and the time and circumstances when it happened (e.g. only when shower runs, random, after sitting idle, after topping up pressure). Take a photo of the display if possible.

2) Try a basic reset: follow the boiler’s documented reset procedure (power off and on or use the reset button/display method). If the message clears and does not return, monitor for recurrence. Resetting is only a temporary measure if there is an underlying fault.

3) Check system pressure on the boiler gauge. Normal running pressure is typically around 1.0–2.0 bar (check your boiler manual for exact range). If pressure is significantly below 1 bar, topping the system up to around 1.2–1.5 bar may resolve transient S.54 events caused by low pressure. Only top up using the filling loop per the boiler manual; close the filling loop valves when finished. If you are unsure how to do this safely, wait for an engineer.

4) Look for visible leaks: inspect under and around the boiler, pipework, and radiators for drips or wet patches. A leak will cause pressure loss and recurring S.54 symptoms.

5) Check mains water supply: ensure the incoming cold-water stopcock to the property and any inlet isolation valve to the boiler are fully open. Restricted mains flow can cause low hot-water flow and trigger waiting periods.

6) Bleed a radiator: if you have cold spots or suspect trapped air, bleed radiators to remove air and then re-check system pressure (topping up again if needed).

Further diagnostic steps to record for the engineer (do not carry out internal repairs yourself)

1) Reproduce the problem if you can: run hot water at a tap or shower and watch the display. Note whether S.54 appears immediately on demand or after some minutes, and whether it clears automatically and how long it takes.

2) Check for associated fault codes: if S.54 is followed or accompanied by F20 or other F‑codes, make a note — these typically point to flow/temperature sensor or safety limiter issues and will require an engineer.

3) If you have previously topped up pressure and the boiler worked for a while, note how long before the code returns. Rapid pressure drops indicate a leak or a faulty expansion vessel/valve.

4) If condensate or external pipework is exposed to frost, ensure condensate pipe is not frozen or blocked (thaw with care); a blocked condensate can cause shutdowns but will usually give a condensate-related fault code.

5) Check for blocked cold mains inlet filter/strainer: some combi boilers have a serviceable inlet filter that can reduce flow; cleaning it requires isolation and is best left to a Gas Safe engineer.

When to call a professional

1) Call a Gas Safe registered engineer if the S.54 message repeats, if it is accompanied by other fault codes (for example F20), if pressure keeps dropping, if you see leaks, or if you are uncomfortable performing the safe checks above. Intermittent faults are best diagnosed with an on-site inspection because they can clear before the engineer arrives; provide the engineer with the notes and photos you collected.

2) Ask the engineer to check system pressure behaviour, expansion vessel, filling loop and isolation valves, inlet filter/strainer, flow/return NTC sensors and flow switch, and any condensate/venting issues. Sensor/NTC faults and internal electrical connections should only be checked and replaced by a qualified engineer.

What to provide the engineer

1) The exact codes shown, times and frequency, photos of the display, what you were doing when it occurred (hot water only, shower, heating on/off), any recent work or changes to the system, and whether topping up pressure temporarily fixed it.

2) Any other symptoms: loss of heating as well as hot water, persistent pressure loss, noises, or visible leaks.

Summary

S.54 is a waiting/status message relating to a detected water/flow deficiency or modulation waiting period. Do the safe initial checks (note codes, reset, check pressure, look for leaks, check inlet water) and collect information. If the code repeats, is accompanied by other F‑codes, or you need to access internal components, contact a Gas Safe engineer for proper diagnosis and repair.