Saunier Duval
DHW Temperature Control / Plate Heat Exchanger Issue
Radiators get hot but domestic hot water temperature is unstable or lukewarm (on combi-type furnace/boiler)
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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
Scaled or partially blocked plate heat exchanger,Faulty DHW NTC sensor,Sticking diverter valve,Insufficient flow through DHW circuit
How to Fix / Troubleshooting
Safety first: Turn off power and close water valves before opening hydraulic components.
- Check DHW flow rate: Ensure taps are not restricted and that flow is within the appliance’s specified range.
- Clean inlet filters: Remove and clean cold water inlet filters to improve flow.
- Sensor check: A technician should test the DHW NTC sensor and replace it if readings are incorrect.
- Descale plate heat exchanger: In hard water areas, the DHW plate heat exchanger may need chemical descaling or replacement.
- Diverter valve service: If the valve is not fully diverting to DHW, it may need cleaning or replacement.
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Repair Difficulty
Hard
4/5
Required Part
DHW Plate Heat Exchanger
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