E20
BWT
External Control / BMS Communication Fault
Heater intermittently shows E20 and stops; may coincide with communication to external controller
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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
Loose or incorrect wiring to external control terminals, Faulty RS485 or dry contact interface, Incorrect external control settings, Damaged communication cable
How to Fix / Troubleshooting
Safety first: Turn off power before adjusting control wiring.
- Check external control mode: Verify in the BWT menu whether the heater is set to remote control or standalone mode, and ensure this matches your installation.
- Inspect communication wiring: Check RS485 or external thermostat wiring for correct polarity, tight connections, and no shorts.
- Temporarily isolate external control: Disconnect external control wiring and set the heater to local control. If E20 disappears, the issue is with the external controller or wiring.
If E20 persists even in standalone mode, the communication interface on the main PCB may be faulty and require professional service.
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Repair Difficulty
Hard
4/5
Required Part
BWT RS485 / External Control Interface
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