Boiler does not ignite, display shows E01 shortly after a heating or DHW demand

Safety first: Turn off the boiler and isolate electrical power at the breaker. Close the gas isolation valve if you smell gas. If you suspect a gas leak, ventilate the area and contact a gas-safe technician immediately.

• Check gas supply: Ensure the gas isolation valve under the ACV boiler is fully open. Confirm other gas appliances in the property work. If not, contact your gas supplier.
• Reset the boiler: Follow the ACV user manual to perform a reset (usually by pressing and holding the reset button on the control panel for a few seconds). Observe if the boiler attempts ignition.
• Inspect ignition electrode (visual only): Remove the front casing only if allowed by local regulations and you are competent. Look at the ignition electrode and cable for obvious cracks, broken ceramic, or loose connections on the ACV burner assembly. Do not bend or file the electrode.
• Check condensate drain: A blocked condensate trap or pipe can prevent ignition. Verify the condensate trap on the ACV heat exchanger sump is not full and the pipe is not frozen or blocked. Clear blockages and refit correctly.
• When to call a professional: If E01 persists after confirming gas supply and performing a reset, a qualified technician should test the ignition electrode, flame sensor, gas valve, and combustion settings using a flue gas analyzer.