Saunier Duval
No demand recognition / flow detection failure
Water heater has power but does not ignite when a hot water tap is opened
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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
Faulty DHW flow sensor, Blocked inlet filter reducing flow below minimum, Stuck flow switch, Incorrect plumbing bypassing the heater
How to Fix / Troubleshooting
Safety first: Turn off power and close the cold water inlet before removing any water components.
Steps:
- Verify flow: Open the hot tap fully and check that water flows strongly. If flow is weak, clean tap aerators and shower heads.
- Clean inlet filter: Remove and clean the Saunier Duval inlet filter on the cold water connection.
- Inspect flow sensor: Remove the flow sensor/turbine and clean any debris or scale. Ensure the turbine spins freely and is installed in the correct direction.
- Check wiring: Confirm the flow sensor connector is firmly attached to the PCB.
Warning: After reassembly, check all joints for leaks under pressure.
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Repair Difficulty
Medium
3/5
Required Part
DHW Flow Sensor
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