Error S.26

Safety first

- If you suspect a gas or combustion problem, turn the boiler off and contact a Gas Safe registered engineer immediately. Do not attempt internal repairs. Ensure you have a working carbon monoxide alarm fitted near the boiler area. Always isolate mains electrical power at the consumer unit before touching any appliance wiring; do not open the boiler casing unless you are qualified.

Initial homeowner checks (safe, simple actions)

1. Note exactly when S.26 appears: during heat demand, after burner shuts down, during hot water, or constantly. Record any other fault codes or unusual sounds.

2. Try a basic reset: follow the boiler display reset procedure in your manual or switch the boiler off at the mains for 1 minute and back on. See if S.26 clears and whether the boiler resumes normal operation.

3. Check the external flue terminal and air intake for obvious blockages: leaves, bird nests, wasps, ice or debris. Clear any external obstruction safely from the outside. A blocked flue can alter pressures and cause overrun behavior.

4. Check the condensate pipe if temperatures are freezing: a frozen condensate can disrupt operation and cause abnormal behavior. Thaw a frozen condensate pipe if safe to do so and re-test the boiler.

5. Listen for fan noise: is the fan running louder than normal or continuing to run for a long time after burner stops? Make a note — useful information for an engineer.

6. Check boiler water pressure and basic settings: very low system pressure or recent servicing can coincide with intermittent faults, though not usually the direct cause of S.26.

If S.26 was a one-off or cleared after reset

- Monitor the boiler for 24-48 hours. If no reoccurrence and no loss of heating/hot water, you can continue normal use but log the event. If it returns, follow the professional steps below.

When to contact a professional (required for diagnosis and repair)

- If S.26 repeats regularly, the fan runs continuously, the boiler locks out, or other fault codes appear.

- If you hear grinding, scraping or abnormally loud fan noise, or if the boiler fails to provide heating/hot water.

What a qualified engineer will check and do (diagnostic and fix steps they will perform)

1. Verify fault history and recreate the fault where possible using the boiler diagnostics and service menu. Retrieve any stored fault logs.

2. Visual and electrical checks without opening combustible components: inspect wiring harnesses and connectors for the fan and hall sensor for corrosion, poor connections or damage.

3. Check fan operation and hall sensor signals: measure fan motor current, RPM signal from the hall sensor, and compare to expected values. Replace hall sensor or re-seat connector if faulty.

4. Inspect flue path and air intake for internal blockages, soot or condensate issues that could affect combustion and require fan overrun for safe purge. Clean and clear as necessary.

5. Test and, if required, replace the fan assembly if motor bearings are worn, the motor is slow to stop, or internal faults exist. Replace any damaged wiring or connectors.

6. Check PCB and control outputs: confirm fan relay/drive signals from the PCB are switching correctly; replace PCB if control electronics are faulty and proven to be the cause.

7. Run the boiler through multiple cycles to confirm the fault no longer appears and verify safe combustion and flue temperatures.

Final notes and homeowner guidance

- Do not attempt internal electrical or gas work yourself. Only a Gas Safe registered engineer should open the boiler or replace combustion or safety parts. When you call an engineer give them the boiler model, S.26 code, whether it is intermittent or continuous, any noises you heard, and whether the flue or condensate was blocked or frozen. If the code was a brief status and the boiler otherwise operates normally you may only need a routine service, but persistent occurrences require professional diagnosis and likely fan, sensor, or PCB work.