E04
Wiser
Boiler Demand Signal / Call-for-Heat Circuit Fault
Thermostat shows E04 and cannot detect the boiler or heating circuit
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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
Open circuit between Heat Hub and boiler call terminals, Incorrect wiring to boiler, Blown internal fuse in Heat Hub, Faulty boiler interface on hub PCB
How to Fix / Troubleshooting
Safety first: All wiring to the boiler and Heat Hub is mains voltage. Isolate power at the consumer unit and verify before touching any terminals.
- Check boiler power: Confirm the boiler has power and its own display is active. If the boiler is off, restore its supply and reset it if necessary.
- Inspect wiring (qualified persons only): With power isolated, open the Heat Hub and boiler wiring compartment. Verify that the call-for-heat terminals (e.g. COM/NO on HubR to boiler room stat terminals) are correctly connected and secure.
- Look for damage: Check for burnt insulation, loose conductors, or signs of overheating on the Heat Hub PCB and terminal block.
- Continuity test: Using a multimeter, test continuity of the call-for-heat cable between the Heat Hub and boiler. Replace damaged cable if open or shorted.
- Reset and test: Restore power, clear any boiler lockouts, and request heat from the thermostat. If E04 persists, the boiler interface circuit in the Heat Hub may be faulty and the hub should be replaced.
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Repair Difficulty
Hard
4/5
Required Part
Wiser Heat Hub boiler interface / call-for-heat terminals
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