Saunier Duval
Diverter Valve Passing / Stuck
Radiators heat when only hot water is requested
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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
Worn diverter valve seals, Sticking diverter valve motor, Debris in hydraulic block, Incorrect installation of diverter cartridge
How to Fix / Troubleshooting
Safety first: Turn off power and allow the system to cool before working on the boiler.
Steps to check:
- Run a hot tap and observe the boiler flow and return pipes; if both heating and DHW circuits warm, the diverter is likely passing.
- Cycle between heating and hot water modes to see if the diverter motor moves (you may hear it).
- Clean any system filter to reduce debris that can jam the valve.
- Replacement or servicing of the diverter valve assembly is typically required and should be done by a qualified engineer.
Warning: Do not dismantle the hydraulic block without draining and isolating the boiler.
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Repair Difficulty
Hard
4/5
Required Part
Diverter Valve Assembly
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