E15
Heatmiser
OpenTherm / Digital Boiler Bus Error
Thermostat shows E15 and cannot detect or control the boiler via OpenTherm or digital bus
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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 wiring to boiler OpenTherm terminals, Reversed polarity on OT+ and OT–, Boiler not configured for OpenTherm, Faulty OpenTherm interface in thermostat or boiler
How to Fix / Troubleshooting
Safety first: Isolate power to both boiler and thermostat before altering any wiring.
Steps:
- Confirm that your boiler supports OpenTherm and that the correct terminals are used (often marked OT, OT+/OT–).
- Check that the two OpenTherm wires run directly between the boiler and the Heatmiser thermostat or interface, with no other devices in between.
- Verify polarity if specified by the manufacturer and ensure there are no shorts or breaks in the cable.
- Enable OpenTherm mode in both the boiler and thermostat installer settings.
- If E15 persists, test with a known-good OpenTherm controller or interface to determine whether the fault lies in the boiler or thermostat.
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Repair Difficulty
Hard
4/5
Required Part
Heatmiser OpenTherm Interface / Smart Thermostat
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