E03
Wiser
Relay / Output Driver Fault
Thermostat displays E03 and heating does not respond to setpoint changes
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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 relay on Heat Hub, Burnt relay contacts, Faulty triac or solid-state output on hub PCB, Overcurrent from connected boiler or zone valve
How to Fix / Troubleshooting
Safety first: The Heat Hub contains live mains. Isolate power at the consumer unit and verify dead before removing the cover. If unsure, contact a qualified electrician or heating engineer.
- Power-cycle the Heat Hub: Turn off power for 60 seconds, then restore. Check if E03 clears on the thermostat after a few minutes.
- Check boiler and valve loads: Ensure the connected boiler, pump, and zone valves are not shorted. Listen for unusual buzzing or burning smell from the Heat Hub or wiring centre. If present, keep power off and call a professional.
- Inspect wiring (qualified persons only): With power isolated, remove the Heat Hub cover. Check that COM/NO/NC terminals for CH and HW are correctly wired and that no strands are bridging terminals.
- Test operation: Restore power and request heat from the thermostat. Observe the Heat Hub relay click and boiler response. If E03 reappears or the relay does not operate, the hub output stage is likely damaged.
- Resolution: Replace the Wiser Heat Hub (HubR) or have the relay/triac replaced by a qualified electronics repairer if supported. Do not bypass or bridge relay contacts as a workaround.
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Repair Difficulty
Hard
4/5
Required Part
Wiser Heat Hub relay board / output driver
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