Display shows flow sensor / no circulation error, burner cycles rapidly or shuts down

Safety first: Turn off power before opening any service valves or electrical covers.

Step-by-step checks:

• Check system valves: Ensure all isolation valves on the flow and return pipes beneath the heater are fully open.
• Clean inlet filters: Many De Dietrich models have mesh filters on the cold water inlet and heating return. Close the relevant isolation valves, unscrew the filter caps, remove and rinse the filters, then reinstall.
• Verify pump operation: With a hot water demand active, listen for the circulation pump. If silent, check the pump’s electrical connector. Some pumps have a manual bleed screw; carefully loosen it to see if the shaft is spinning (have a cloth ready for small leaks).
• Flow sensor inspection: Locate the domestic hot water flow sensor (often on the cold inlet). Check for loose wiring. If accessible, remove and inspect for debris or limescale obstructing the turbine or paddle.

When to call a professional: If the pump is seized, the plate heat exchanger is blocked with limescale, or the flow sensor is defective, professional replacement is recommended.