Water heater does not ignite; display shows error 01 shortly after a hot water demand.

Safety first: Turn off electrical power to the water heater and close the gas shut‑off valve before removing any covers. Wait for the unit to cool.

Steps to check:

• Verify gas supply: Ensure the main gas cock to the Immergas water heater is open and that other gas appliances in the home work correctly. If there is no gas supply, contact your gas provider.
• Inspect burner area: Remove the front cover according to the user/installation manual. Check the main burner for dust, rust flakes, or spider webs. Gently vacuum and clean with a soft brush—do not use metal tools that can deform the burner.
• Check ignition electrode: Locate the ignition electrode near the burner. Inspect the ceramic insulator for cracks and the tip for heavy oxidation. Clean the tip with fine emery cloth. Ensure the electrode gap and position match the service manual. Re‑seat the ignition cable firmly on the electrode and on the control board.
• Check flame detection electrode: On many Immergas models, the flame sensor is combined with or next to the ignition electrode. Clean it as above and ensure it is properly grounded to the burner.
• Reset the appliance: Restore power and gas, then perform a reset using the front panel reset button. Open a hot water tap and observe ignition. If error 01 reappears, the gas valve coil or control board may be faulty.

When to call a technician: If you smell gas, if the burner does not ignite despite confirmed gas supply, or if you are not trained to work on gas valves or control boards, stop and contact an authorized Immergas service center.