E15
Wiser
OpenTherm / Digital Boiler Communication Fault (where supported)
Thermostat shows E15 and the boiler cycles rapidly or does not respond correctly
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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
Incorrect OpenTherm wiring, Incompatible boiler protocol, Damaged OpenTherm interface on Heat Hub, Reversed polarity on OT terminals
How to Fix / Troubleshooting
Safety first: OpenTherm connections are typically low voltage but may be inside mains compartments. Isolate boiler and Heat Hub before opening covers.
- Verify compatibility: Confirm that your boiler supports OpenTherm and that Wiser is configured to use it (if applicable).
- Check wiring: With power off, ensure the OpenTherm + and - wires are correctly connected between the Heat Hub OT terminals and the boiler OT terminals.
- Inspect cable: Look for damage or crushing along the cable route.
- Switch to relay mode (test): If possible, temporarily configure the Heat Hub to use simple on/off relay control instead of OpenTherm to see if heating stabilises.
- If E15 persists in OT mode: The OpenTherm interface on the Heat Hub or boiler may be faulty. Consult a heating engineer; replacement of the Heat Hub or boiler control board may be required.
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Repair Difficulty
Hard
4/5
Required Part
Wiser Heat Hub OpenTherm interface
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