Navien NHB-055, Service Manual

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NHB Service Manual 75 Version 1.0
4.9.11 Secondary Heat Exchanger
Part Check Point
Function
1. Main part for heat transfer from the burner.
2. There are multiple paths of water pipes on the heat exchanger as well as inside the combustion
chamber which minimizes heat loss.
Failure Event
1. Water and/or exhaust gas leakage through a crack.
2. Improper heat transfer can cause the water in heat exchanger to boil.
Effects
1. Exhaust gas leakage.
2. Excessive heating of the water that produces boiling noises.
Error Code E016, E030, E047
Diagnostic
1. Visual inspection: Check if there is a crack on the surface of heat exchanger.
2. Sound inspection: Check if boiling occurs.