Error S.24

Safety precautions:

1) If you smell gas: do not operate electrical switches, do not light matches, open windows and doors, turn off the gas at the meter or isolation valve if safe to do so, leave the building and call the emergency gas number immediately.

2) If the boiler is behaving badly (continuous flame symbol, loud noises, error lockout), switch the boiler to the off position and isolate electrical supply if you are uncomfortable, but do not open or dismantle the boiler or attempt to work on gas components.

3) Only perform visual and non-intrusive checks. Any work inside the casing, on gas fittings, ignition components, or PCB must be done by a Gas Safe registered engineer.

Initial checks a homeowner can do:

1) Record the exact error code (S.24) and note when it appears (e.g. when turning on a hot tap). This helps the engineer.

2) Try a single reset: follow the boiler’s reset procedure (press and hold reset for up to 10 seconds). Wait to see if the boiler attempts to relight and if the error returns. Do not repeatedly reset more than once or twice if the fault persists.

3) Check gas supply to the property: confirm other gas appliances (hob, gas fire) work. If all gas is off at the meter or you suspect an interruption from the supplier, contact the supplier.

4) Check the condensate discharge outside (in cold weather the condensate pipe can freeze) and make sure it’s not blocked; if frozen, thaw with warm (not boiling) water or a warm cloth. A blocked condensate can prevent normal burner operation.

5) Check the boiler display for any other linked errors or messages (e.g. low water pressure message, F‑codes) and check the heating pressure gauge. Top up the system only if you know how and the pressure is below recommended levels (typically around 1–1.5 bar) — follow the boiler manual for topping-up steps.

6) Check the flue terminal area for obvious blockages (birds' nests, debris) from outside; do not reach into or remove flue parts yourself.

Specific diagnostic and next-step guidance (what an engineer will normally check and what to prepare):

1) If the reset does not clear S.24, stop further DIY attempts. Prepare to call a Gas Safe engineer and provide the boiler model, serial number, error code S.24, and the circumstances when it occurred.

2) The engineer will check the ignition sequence and flame detection: test spark generator, electrode condition and alignment, ignition lead continuity, and flame sensor signal. Homeowners should not attempt these checks.

3) They will test gas supply pressure to the appliance and check the gas valve operation and resistance. They may measure gas valve coil resistance (professional equipment required).

4) They will inspect the fan and any flue or pressure switches for correct operation and ensure no blockages in the flue or air intake.

5) They will check the condensate trap and discharge, along with any sensors or interlocks related to DHW demand (flow/impeller sensors, NTC sensors) and relevant wiring harness connections to the PCB.

6) If electrical faults are suspected, the engineer will check the PCB and connections; in some cases a replacement part (electrode, ignition lead, gas valve, fan, NTC sensor or PCB) may be required.

When to call a professional and what to tell them:

1) Call a Gas Safe registered engineer whenever S.24 persists after a single reset, when you cannot identify a safe external cause (gas supply, frozen condensate, flue blockage), or if you are unsure. Do not try to repair internal components yourself.

2) Provide: boiler model and serial, exact error code S.24, whether the boiler locked out, whether you tried resetting and what happened, recent service history, and whether other gas appliances work.

3) If you suspect a gas leak or if the boiler behaves unsafely, isolate gas and electrics, leave the property, and call emergency services or your gas supplier.

Summary reminder: S.24 means a burner-related fault in DHW mode. Safe, simple checks (reset once, check gas supply, check condensate and flue for obvious external blockages, check system pressure) can be done by the homeowner. Any internal diagnostic or repair involving gas, ignition, or wiring must be performed by a Gas Safe engineer.