E21
Trane
Ventilation System Communication Error
Thermostat displays E21 and ventilation/ERV control is not available
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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
Disconnected Trane energy recovery ventilator (ERV) or ventilation module, Miswired ventilation control terminals, Failed ERV control board, Incorrect ventilation configuration in thermostat
How to Fix / Troubleshooting
Safety: Disconnect power to the ERV or ventilation unit before opening any panels.
- Step 1 – Confirm ERV presence: Verify that a Trane ERV or ventilation system is installed. If not, disable ventilation control in the thermostat installer setup.
- Step 2 – Inspect low-voltage wiring: At the ERV and indoor unit, check the ventilation control terminals and wiring harness for loose connections or damage.
- Step 3 – Check ERV power: Ensure the ERV breaker or plug is energized.
- Step 4 – Reconfigure ventilation: In the thermostat installer menu, select the correct ventilation equipment type and control mode.
- Step 5 – If E21 remains: The ERV control board or communication interface may be defective and require replacement.
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Repair Difficulty
Medium
3/5
Required Part
Trane ERV / Ventilation Control Board
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