Error E.01 – .11

Safety first

1) If you smell gas, or your CO alarm is active, get everyone out of the property immediately and call the emergency gas number or emergency services. Do not switch electrical items on or off, do not use phones inside the building, and do not attempt any repairs.

2) Turn off the boiler at the isolator or mains and switch off electrical supply if you need to work near the appliance for any checks that require access to the casing. However, do not remove the boiler casing or attempt internal repairs — internal work must be done by a Gas Safe engineer.

Initial homeowner checks (safe, non-intrusive)

1) Note the exact code displayed (E.01 through E.11) and whether anything else appears on the display. Take a photo for the engineer.

2) Check the boiler’s reset procedure and try a single reset: with the boiler powered, press and hold the reset/selector to R for about 3–5 seconds (follow your model’s instructions). Wait to see if the boiler starts normally. Do not keep repeating resets more than once or twice.

3) Check the flue terminal outside for obvious obstructions: birds’ nests, leaves, debris, or snow/ice. If you can safely reach the flue from ground level and there is a visible obstruction, remove it carefully. If high or unsafe to reach, do not attempt — call an engineer.

4) Look for sources of strong external draught: open windows, nearby extractor fans, dryer vents, or temporary wind funnels that could be blowing directly into the flue. If you suspect a sudden wind/draught problem, close nearby windows/doors and try the reset again.

5) Check that the gas supply is on (test another gas appliance such as a hob). Check the boiler has mains power and that any room thermostat or programmer is calling for heat.

6) Confirm your CO alarm is fitted and working. If you don’t have one, fit one as soon as possible.

Diagnostic notes and what to tell your engineer

1) If the error clears after a single reset and does not return, monitor the boiler for recurrence. If it returns, record when it happens, whether it happens only in windy weather, and any noises (grinding, rattling) from the boiler.

2) If the flue was blocked and you cleared it and the fault persists, or if the flue appears unobstructed but the error remains, this suggests an internal fan fault or gas/air unit problem that requires a Gas Safe engineer.

3) When you call the engineer, give them the exact code (E.01–.11), any other displayed messages, symptoms you observed (noises, intermittent operation, lockouts), whether the fault is constant or weather-related, and any reset attempts you made.

What a professional will check (do not attempt yourself)

1) Electronic checks and fan motor testing: measure fan speed and motor performance, inspect fan wiring and connector continuity, and confirm correct control signals from the PCB.

2) Flue and air pressure switch checks: confirm the air pressure switch and flue thermistor are working and that there is correct differential pressure during fan operation.

3) Gas/air unit inspection: inspect and, if necessary, replace the gas/air (venturi) unit or fan assembly and calibrate the burner and sensors.

4) Fit anti-draught measures if external draught is confirmed to be the cause (specialist cowl or relocation advice).

Final guidance

1) Do not attempt to access or replace fan components, the gas valve, or the gas/air unit yourself — these are live gas and electrical components requiring a Gas Safe registered engineer.

2) If the fault persists after the safe checks above, or if the boiler locks out repeatedly, keep the boiler off and arrange an urgent Gas Safe engineer visit. Provide them with the code, photos, and the history of what you tried to speed diagnosis.

3) Avoid repeated resets — once or twice for diagnosis is acceptable but frequent resetting can mask or worsen a fault. If in doubt, call a professional.