Glow-worm
DHW Priority / Diverter Valve or Sensor Fault
Boiler provides heating but no domestic hot water on a combi model
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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 diverter valve in heating position, Faulty domestic hot water flow sensor, Blocked plate heat exchanger, DHW NTC sensor failure
How to Fix / Troubleshooting
Safety: Isolate power and water before removing covers or sensors. Hot water can scald; allow to cool.
- Check hot tap flow: Open a hot tap fully. If the boiler does not respond (no burner symbol or flame), the DHW flow sensor may not be detecting flow.
- Check for partial heating: If radiators get hot when a hot tap is opened, the diverter valve may be stuck in heating mode.
- Engineer tasks:
- Test and replace the DHW flow sensor/turbine.
- Inspect and free or replace the diverter valve cartridge or motor.
- Clean or replace a blocked plate heat exchanger if DHW temperature is unstable.
DHW faults on combis often require internal component replacement; use a qualified engineer.
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Repair Difficulty
Hard
4/5
Required Part
DHW Flow Sensor
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