Boiler does not ignite, display shows E01 and heating and hot water are unavailable.

Safety first: Switch the boiler off at the control panel and isolate the electrical supply. Close the gas isolation valve to the boiler. Do not work on gas-carrying components unless you are a qualified gas engineer.

User-level checks:

• Verify that the gas supply to the property is available (check other gas appliances).
• Check that the boiler gas isolation valve is fully open.
• Reset the boiler using the reset button as described in the Chaffoteaux manual. Observe if E01 reappears.
• Ensure the flue terminal is not blocked by debris, snow, or vegetation.

Technical checks (for qualified personnel only):

• Inspect and clean the burner and injectors; remove any soot or debris.
• Check the ignition electrode and flame detection electrode for cracks, carbon build-up, or incorrect gap; clean or replace as needed.
• Verify correct wiring and continuity of the ignition cable and electrode leads.
• Measure gas valve coil resistance and verify that the control board is sending voltage to the gas valve during ignition.
• Check gas inlet pressure and burner pressure against Chaffoteaux specifications and adjust the gas valve if required.

If the boiler still shows E01 after these checks, the gas valve or control board may need replacement. This work must be carried out by a certified technician.