Ariston
DHW Priority / Diverter Valve Fault
Boiler runs for heating but hot water is lukewarm or cold
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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
Diverter valve stuck in CH position, Blocked DHW plate heat exchanger, Faulty DHW flow sensor, Incorrect boiler settings
How to Fix / Troubleshooting
Safety: Turn off power and isolate water before removing any water components.
- Check boiler display: Many Ariston models show a tap symbol when DHW is demanded. If this does not appear when a hot tap is opened, the DHW flow sensor may be faulty.
- Diverter valve test: When a hot tap is opened, the CH flow pipe should cool and DHW pipes should heat. If CH stays hot and DHW cold, the diverter valve is likely stuck.
- Descale plate heat exchanger: If DHW is only lukewarm at high flow, the DHW plate heat exchanger may be scaled and require descaling or replacement.
- Engineer repair: Diverter valve and plate heat exchanger work should be done by a qualified engineer.
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Repair Difficulty
Hard
4/5
Required Part
Diverter Valve Assembly
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