Error S.01

Safety precautions:

- Do not open the boiler casing, attempt internal electrical or gas repairs, or tamper with combustion components. These actions are dangerous and must only be done by a Gas Safe registered engineer.

- Before any external checks isolate external controls where appropriate and ensure hands are dry and you are on a stable surface when inspecting the boiler.

- If you smell gas or suspect a gas leak, leave the property immediately and call the gas emergency number for your area; do not operate electrical switches or the boiler.

Initial homeowner checks you can safely do:

1. Read the display carefully and note the exact code(s) and any accompanying messages. Take a photo of the display for a technician if needed.

2. Check whether heating is actually required: verify room thermostat set point, TRV positions, and that any external controller (timer/Smart stat) is calling for heat. If there is no demand, S.01 may simply be a transient status when the boiler last started.

3. Check boiler status after a normal restart: press the boiler fault-clear/reset button for one second (refer to your manual) or switch the boiler off at the external isolation switch, wait 30 seconds and switch it back on. Observe whether S.01 appears briefly and the boiler then ignites normally.

4. Confirm mains power and gas supply: ensure the boiler isolation switch is on, the gas meter and isolator cock are open, and there is no external interruption to gas supply.

5. Check visible obstructions: inspect the external flue terminal to ensure it is clear of debris, nests, snow or ice. A blocked flue can prevent the fan/flue system from operating correctly.

6. Check condensate and external pipes (in cold weather): a frozen condensate or blocked drain can cause start-up issues. Thaw a frozen condensate pipe safely (warm water) if you are confident; otherwise call a pro.

7. Check system pressure: look at the boiler pressure gauge. Typical operating pressure is around 1–1.5 bar cold. Very low pressure can prevent normal operation. Do not attempt to add water unless you understand your specific system—consult the manual or an engineer if unsure.

Diagnostic steps and what they indicate (homeowner vs. professional):

- If S.01 only appears briefly and heating works: no action required. Log occurrence and monitor.

- If S.01 repeats and boiler fails to proceed to ignition or you see F.32 (fan fault) or ignition-related faults: this strongly suggests a fan, fan wiring/hall sensor, flue blockage, or PCB/electronics issue. At this point stop further DIY checks and contact a Gas Safe engineer.

- If the boiler shows S.01 and you hear no fan noise when heat is demanded: check for external flue blockages and power to the boiler. If power and flue are OK, do not open the casing; this requires professional electrical/fan testing.

- If the fan runs but the boiler still fails to ignite: the problem may be downstream (ignition, flame detection, gas supply) — a qualified engineer must carry out tests and safe repairs.

Professional checks and likely fixes (for the engineer, do not attempt yourself):

- Verify error history and live monitor logs, run diagnostics to replicate fault and measure fan supply voltage and control signals.

- Inspect fan connector, wiring harness and hall sensor; measure fan motor continuity and hall sensor signals. Replace fan assembly or hall sensor if faulty.

- Check flue and air supply path for partial blockages and clean if sooted or obstructed.

- Test PCB outputs and inputs related to fan control; repair or replace PCB if defective.

- Check related safety devices (STB, temperature sensors, condensate trap) and replace or repair as required.

When to call a professional and what to provide:

- Call a Gas Safe registered engineer whenever the boiler does not progress past S.01 to ignition, when you see accompanying fault codes (for example F.32), when you smell gas, or when you are unsure how to proceed.

- When you call, provide the exact fault code(s), whether S.01 is constant or intermittent, what you heard or observed (no fan sound, clicking, lockouts), the boiler serial number and any recent service history. Provide the photo of the display if you took one.

Final notes:

- S.01 is usually informational when the boiler is starting the fan in heating mode; brief appearances with normal operation are not a fault. Persistent S.01, repeated start failures, or additional fault codes indicate a fault that requires professional diagnosis and repair. Do not perform internal repairs yourself; for safety and warranty reasons use a qualified Gas Safe engineer.