No hot water at all, burner does not start when hot tap is opened

Safety first: Turn off power before removing covers or filters.

Step-by-step checks:

• Check cold supply: Confirm that cold water flows strongly from the hot tap (cold side of mixer). Weak flow indicates a supply or filter issue.
• Clean inlet filter: Close the cold inlet isolation valve under the heater. Remove the cold inlet filter plug, extract the mesh filter, rinse thoroughly, and reinstall. Open the valve slowly and check for leaks.
• Observe display: On many De Dietrich models, a tap symbol or flow rate appears when demand is detected. If nothing appears, the flow sensor or wiring may be faulty.

When to call a professional: If cleaning filters does not restore operation, the flow sensor or diverter valve may need replacement.