This error code appears when the vent damper fails to close properly. It happens when the damper, wire harness, or control board are faulty.
How do I fix it?
- Make sure there is no voltage on P6-5.
- Adjust the thermostat or disconnect TT terminals.
- Check the 24Vac power supply between ground and P6-5.
- If there is no voltage, try to restart the boiler.
- If the 25Vac is there, disconnect the vent damper wiring from the control board and check the 24Vac between ground and P6-5.
- If there is voltage, it is a control issue. Replace the control board.
- If there is no voltage, it is a wire harness or damper issue. If these are faulty, replace or repair them.