E2
Buderus
Communication Fault with Room Thermostat or Control
Furnace shows E2, no response to thermostat, burner does not start
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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
Broken or shorted thermostat cable, Incorrect polarity on Buderus EMS/RC thermostat bus, Faulty room controller, Control board communication failure
How to Fix / Troubleshooting
Safety: Turn off power before working on low-voltage wiring.
Steps:
- Check thermostat display: Ensure the Buderus room controller or thermostat is powered and not showing its own error.
- Inspect wiring: At the furnace control, verify that the thermostat or EMS bus wires are firmly connected to the correct terminals. Look for damaged insulation or shorts between conductors.
- Polarity: On Buderus EMS/RC systems, maintain correct polarity (e.g., + and -). Reversed wires can cause E2.
- Bypass test (simple thermostats only): If using a basic on/off thermostat, temporarily jumper the R and W (or equivalent) terminals at the furnace to see if the unit responds. Remove jumper after test.
If E2 persists with correct wiring and a known-good thermostat, the main control board may require replacement by a professional.
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Repair Difficulty
Medium
3/5
Required Part
Buderus Control Board (Main PCB)
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