E23
Remeha
OpenTherm communication fault
Display shows E23, furnace does not respond to external control
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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
Incorrectly wired OpenTherm thermostat, Faulty OpenTherm controller, Reversed polarity on OT terminals, Faulty OpenTherm interface on PCB
How to Fix / Troubleshooting
Safety first: Turn off power before working on control wiring.
- Verify wiring: Check that the two OpenTherm wires are connected to the correct OT terminals on both the furnace and the controller. Polarity usually does not matter, but follow Remeha instructions.
- Check cable type: Use suitable low-voltage cable and avoid running OT wires alongside mains cables to reduce interference.
- Controller test: If possible, test with a known-good OpenTherm controller to rule out a faulty thermostat.
- Fallback mode: Temporarily configure the furnace for simple on/off control (if supported) to restore heating while OT is diagnosed.
- PCB interface: If wiring and controller are good, the OpenTherm interface on the PCB may be defective and require replacement.
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Repair Difficulty
Medium
3/5
Required Part
OpenTherm Interface (on Main PCB)
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