Water heater does not ignite; burner does not start, display shows E01 shortly after a hot water demand.

Safety first: Turn off the main gas cock to the Weishaupt water heater and isolate electrical power at the breaker before removing any covers. Allow the unit to cool.

• Check gas supply: Verify the external gas shut-off valve to the Weishaupt heater is fully open. Confirm other gas appliances in the home work. If gas pressure seems low, contact your gas supplier.
• Inspect ignition electrode: Remove the burner access panel. Locate the Weishaupt ignition electrode near the burner head. Check for cracks, heavy soot, or scale. Clean gently with fine emery cloth and ensure the electrode tip gap and position match the service manual (typically a few millimeters above the burner surface).
• Clean flame sensor: On many Weishaupt units the flame sensor is combined with or adjacent to the ignition electrode. Carefully clean the sensor rod with fine abrasive pad to remove oxidation.
• Check wiring: Inspect the ignition cable from the control board to the electrode for burns, cuts, or loose push-on connectors. Reseat connectors firmly.
• Reset and test: Restore power and gas, then reset the heater according to the front panel instructions. Call for hot water and observe ignition. If E01 returns, the gas valve assembly or control board may be defective and a qualified Weishaupt technician should test gas pressures and valve operation.