Water heater produces no hot water at all; display is on but burner never starts and no error code is shown.

Safety: Turn off power and close the cold water inlet before removing any water connections.

• Check hot water taps: Confirm that there is adequate flow at the hot taps. Very low flow may not trigger the Weishaupt flow sensor.
• Clean inlet filter: Remove and clean the cold water inlet filter at the heater to restore flow.
• Inspect DHW flow sensor: Remove the flow sensor assembly and check that the turbine spins freely. Clean or replace if jammed.
• Combi diverter valve: On combi models, ensure the diverter valve is not stuck in heating position. A technician may need to remove and service or replace the valve.
• Demand wiring: If an external demand contact is used, verify that it closes when hot water is requested.