Heatmiser
Hot Water Channel Control Fault
Thermostat cannot control hot water cylinder even though heating zones work
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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
Hot water relay not wired, Incorrect configuration of HW channel in wiring centre, Cylinder thermostat wired to bypass Heatmiser, Faulty HW relay on wiring centre
How to Fix / Troubleshooting
Safety first: Isolate power to the wiring centre and boiler before working on hot water controls.
Steps:
- At the Heatmiser wiring centre (e.g., UH1), verify that the hot water output is wired to the cylinder valve or boiler HW input.
- Check that the Heatmiser thermostat assigned to hot water is correctly configured as a hot water channel in the installer settings.
- Ensure the cylinder thermostat is wired in series with the Heatmiser control, not bypassing it.
- Test the HW relay output with a multimeter when calling for hot water; if no output, the wiring centre relay may be faulty and require replacement.
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Repair Difficulty
Hard
4/5
Required Part
Heatmiser Wiring Centre (Hot Water Relay)
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