Navien NHB-055 Service Manual page 90

Failure mode
Flame sensing error
Repeated
ignition-out
Flame loss and Check if there are any
noise occurs at blockages in the gas
ignition
Improper air
Rainwater intrusion
intake air supply
Other trouble
90 NHB Service Manual
Cause
1. Check the location of the flame, if there is any deformation or foreign substance, repair
or replace the part.
2. Check the flame rod wire for proper connection and/or damage.
3. Check the grounding to the boiler case to verify proper grounding at the outlet.
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Measuring flame current
Ignition failure will occur if the gas orifices are clogged.
Remove the gas inlet pipe and check the orifice plate.
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orifice plate.
Check if rainwater has collected inside the unit from an improperly installed air intake pipe.
Screw loosening Tighten the ground connection screws on heat exchanger.
Defective PCB If the issue continues despite checking above items, replace the PCB.
If the ground wire is improperly connected or not making a good connection,
remove and reattach the ground wire ensuring good contact with the case.
Or use a multi-meter to measure the flame sensing current (normally over 3~4 μA).
Check method
Grounding wire position
Version 1.0