Er5
Eurotronic
Bus Communication Error with External Module
Display shows 'Er5' and thermostat cannot detect or control external relay module.
Advertisements
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.
Advertisements
Possible Causes
Broken bus cable between thermostat and Eurotronic relay module, Incorrect bus polarity, Loose bus terminals, Defective bus transceiver on PCB
How to Fix / Troubleshooting
Safety: Isolate mains power before touching any relay module wiring.
- Check wiring: Verify that the bus wires (often low-voltage, marked BUS+, BUS− or similar) are connected to the correct terminals on both thermostat and relay module.
- Tighten terminals: Tighten all bus terminal screws and ensure no copper strands are shorting between terminals.
- Check cable continuity: With power off, use a multimeter to check continuity of each bus conductor from thermostat to relay module.
- Short cable test: Temporarily connect the thermostat to the relay module with a short, known-good cable. If Er5 clears, replace the original cable.
- Replace module/thermostat: If wiring is correct and Er5 persists, either the relay module or thermostat bus interface is defective. Replace the faulty unit.
Advertisements
Repair Difficulty
Hard
4/5
Required Part
Bus Interface / External Relay Module
Check Price on Amazon
We may earn a commission from links on this page.
Advertisements