P1 appears; heater may not respond to hot water demand or shows incorrect flow.

This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.

If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.

Possible Causes

Flow sensor out of calibration, Partial blockage in inlet filter, Incorrect minimum flow setting, Faulty flow sensor electronics

Safety: Close water supply and relieve pressure before removing filters.

Clean inlet filter: Remove and rinse the cold water inlet filter at the heater.
Check minimum flow: Ensure taps are opened sufficiently; some Junkers models require a minimum flow to start (e.g., 2–3 l/min).
Reset calibration (if available): Some models allow a flow sensor calibration via service menu; follow the installation manual.
Replace sensor: If P1 persists and flow is good, the flow sensor may need replacement.

Medium 3/5

DHW Flow Sensor

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