Defro
Unwanted Heating / Diverter Valve Bypass
Radiators get hot even when there is no call for heating, especially when hot water is used.
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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 or leaking Defro diverter valve, Incorrect wiring of external controls, Debris in hydraulic block causing cross-flow, Faulty diverter motor head on Defro combi boiler
How to Fix / Troubleshooting
Safety: Allow radiators to cool before working on valves or pipework.
- Check controls: Ensure the room thermostat and programmer are not calling for heat and that the Defro boiler is not in a constant heating mode.
- DHW test: Run a hot tap and feel the heating flow pipe from the boiler. If it gets hot during DHW-only demand, the diverter valve is likely passing.
- Exercise valve: With power off, manually move the diverter valve (if it has a manual lever) several times to free it, then retest.
- Replace diverter: If the problem persists, the Defro diverter valve cartridge or motorized head should be replaced.
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Repair Difficulty
Hard
4/5
Required Part
Defro diverter valve assembly
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