Navien NCB-24LSWE, Service Manual

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104 NCB Service Manual Version 1.0
Testing method
Fault Possible causes Testing method
110E
Exhaust blockage
Intake air supply /
exhaust flow error
1. If 110E occurs intermittently during ignition or combustion, compare the
standard speed with the current speed at min/max combustion. If the current
speed is higher than normal, check the following:

Air supply / exhaust pipes for blockage.

Blocked condensate drain

Broken or blocked air pressure sensor hose.
2. Replace the old PCB with the latest version.
Condensate drain
error
Condensate drain
error
Exhaust air is blocked due to condensate drain faults.

Check if the condensate hose or the siphon is frozen.

Check if the condensate hose is kinked.

Remove the bottom of the trap and verify it is not blocked.
Defective air
supply/exhaust
flue
Deformed or
blocked flue
1. Check the exterior of the flue for damage and obstructions.
2. Check if rainwater has accumulated in vertically installed sections of the air
intake.
Exhaust gas
enters the air
supply pipe
If exhaust gas enters the air supply pipe, combustion faults may cause E110.

Check the installation of the flue.
5.2.12 Error 205
Error conditions and checklist
Error Description
E205
Heat exchanger
output
temperature
sensor open
If an error (open: -10°C or lower) in the heat exchanger input temperature sensor is detected, the system
displays ‘205E’ on the front panel. If this occurs, the boiler shuts down.
Checklist
1. Check if the heat exchanger output temperature sensor connector is wet due to any reason,
including leakage.
2. Replace the defective heat exchanger output temperature sensor.
3. Check the circulation pump’s operating status and the flow rate in the space heating lines.
4. Test the voltage at the PCB to verify the correct voltage at the pump. If there is no voltage, bleed the
air from the system before resetting the unit. If the error condition persists, replace the pump.