Error S.23

Safety precautions:

1. If you smell gas anywhere in the house: do not operate electrical switches, ventilate the area, leave the property and call the emergency gas number immediately.

2. If the boiler is showing S.23 and there are no gas smells, treat the boiler as potentially unsafe for combustion repairs—do not open the combustion chamber or attempt to access ignition electrodes or gas valve components. Always call a Gas Safe registered engineer for internal work.

3. Turn off electrical power to the boiler before doing any external checks if you are unsure, and always follow the boiler manufacturer’s safety instructions.

Initial checks a homeowner can safely do:

1. Note the exact error code (S.23), when it occurred and any recent events (power cut, gas work, freezing weather). Take a photo of the display and write down the boiler serial number if possible.

2. Try a basic reset: press and hold the boiler reset button for the time recommended in your manual (usually a few seconds). If the code clears and the boiler operates normally, monitor it. If S.23 returns, further investigation is required.

3. Check the gas supply to your home and boiler: make sure other gas appliances (hob, gas fire) are working. Check the boiler’s gas isolation valve (usually a lever) is in the open position. If your gas supply is off, contact your gas supplier.

4. Inspect the outside flue and air intake terminals for obvious blockages (nests, leaves, snow/ice) from ground level only. Clear minor external debris if it is safe to do so. Do not force or dismantle terminals.

5. If you have a condensate pipe termination outside, check it isn’t frozen or blocked (common in cold weather). Thaw frozen condensate pipes with warm water or a frost-safe measure; avoid pouring boiling water on plastics.

6. Ensure the boiler has electrical power and the mains switch or fuse has not tripped. Check household fuses if the boiler has no display.

Specific diagnostic/fix steps (what the engineer will typically do and what you can prepare for):

1. If S.23 persists after basic checks and reset, stop trying resets and arrange a Gas Safe engineer. When you call, provide the engineer with the error code (S.23), when it started, any recent resets and the boiler model and serial number.

2. The Gas Safe engineer will check gas supply pressure to the appliance, the position and operation of the gas isolator, and confirm correct gas type and pressure at the valve.

3. They will test ignition components: ignition transformer, ignition lead, electrode gap and condition, and the ionisation/flame detection circuit. They may replace ignition leads/electrodes if faulty.

4. The engineer will inspect the burner and combustion chamber for condensate or contamination, check the condensate trap and discharge, and verify the flue and air intake for any obstruction or recirculation issues.

5. They will test control components and sensors: the mass flow sensor, PCB ignition control outputs, earthing/grounding and any wiring harness for continuity or intermittent faults.

6. If the gas valve or gas valve assembly is suspected, they will test its operation (resistance, actuation and pressure) and replace it if required. They will also verify the boiler’s software/parameter settings related to gas valve calibration where applicable.

7. After repairs or replacements, the engineer will perform safe-lighting checks, combustion and spillage tests, verify flame stability, and confirm no faults are present before returning the boiler to service.

Final points and when to call a professional:

1. Because S.23 concerns ignition and flame detection, it is a safety-related fault and most reliable, safe repairs require a Gas Safe registered engineer. Do not attempt internal electrical or gas-component repairs yourself.

2. If the fault returns after an engineer visit, record the circumstances and inform the engineer; intermittent faults often require thorough wiring and PCB checks.

3. If you have any doubt about safety (persistent fault, unusual smells, soot, blackening, poor combustion odour) turn the boiler off, ventilate, and contact a Gas Safe engineer immediately.

Prepare information for the engineer: error code (S.23), boiler model and serial number, photos of the display and flue terminals, and a short timeline of events leading to the fault. This helps speed diagnosis and repair.