Worcester
DHW Priority / Plate Heat Exchanger Flow Fault
Radiators get hot but domestic hot water is lukewarm or cold on a Worcester combi 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
Blocked plate heat exchanger, diverter valve not fully moving to DHW position, scaled DHW side, faulty DHW flow sensor
How to Fix / Troubleshooting
Safety first: Water may be hot; take care when testing taps.
Homeowner checks:
- Run a single hot tap fully open and see if the boiler fires and stays on.
- Ensure cold inlet and hot outlet isolation valves under the boiler are fully open.
Engineer actions:
- Check DHW flow rate and verify the DHW flow sensor is detecting demand.
- Inspect and clean or replace the plate heat exchanger if restricted by scale or sludge.
- Test the diverter valve motor and mechanism; replace or service if not fully diverting to DHW.
Restoring DHW performance often involves descaling or replacing the plate heat exchanger on Worcester combis.
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Repair Difficulty
Hard
4/5
Required Part
Plate Heat Exchanger
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