Worcester Bosch
Insufficient DHW Output / Modulation Fault
Boiler runs but produces lukewarm hot water only, even at low flow rates.
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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
Gas valve not opening fully, Incorrect boiler DHW power setting, Partially blocked plate heat exchanger, Faulty DHW NTC giving false high reading
How to Fix / Troubleshooting
Safety first: Gas adjustments must be done by a Gas Safe engineer.
User checks:
- Ensure hot water tap is fully open and that cold inlet isolation valves are fully open.
- Check that the boiler is set to maximum hot water temperature on the control panel.
Engineer actions:
- Check the plate heat exchanger for blockage and descale or replace if necessary.
- Verify gas rate and burner pressure at maximum DHW demand; adjust or replace the gas valve if not achieving rated output.
- Test the DHW NTC sensor for correct readings; replace if it is falsely reporting high temperature.
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Repair Difficulty
Hard
4/5
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