Junkers
No Demand Detection / Flow Activation Failure
No hot water at any tap; display is on, but burner does not start and no error code is shown.
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Safety Warning
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.
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Possible Causes
Stuck DHW flow sensor turbine, Blocked cold water inlet filter, Very low mains water pressure, Faulty microswitch or Hall sensor on water section
How to Fix / Troubleshooting
Safety: Close the cold water inlet and relieve pressure before opening water components.
- Check other taps: Confirm cold water supply is available elsewhere in the house.
- Clean inlet filter: Remove and rinse the inlet filter at the heater's cold water connection.
- Operate tap fully: Open the hot tap fully to ensure sufficient flow to trigger the heater.
- Inspect flow sensor: If accessible, remove the flow sensor/turbine and clean debris or scale. Ensure it spins freely.
- Test microswitch (older hydraulic models): On older Junkers hydraulic water heaters, verify that the water section lever actuates the microswitch when a tap is opened.
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Repair Difficulty
Medium
3/5
Required Part
DHW Flow Sensor / Water Section Microswitch
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