90 NHB Service Manual
Version 1.0
Failure mode
Cause
Check method
Repeated
ignition-out
Flame sensing error
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.
●
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).
Measuring flame current
Grounding wire position
Flame loss and
noise occurs at
ignition
Check if there are any
blockages in the gas
orifice plate.
Ignition failure will occur if the gas orifices are clogged.
●
Remove the gas inlet pipe and check the orifice plate.
Improper air
intake air supply
Rainwater intrusion
Check if rainwater has collected inside the unit from an improperly installed air intake pipe.
Other trouble
Screw loosening
Tighten the ground connection screws on heat exchanger.
Defective PCB
If the issue continues despite checking above items, replace the PCB.
Summary of Contents for NHB-055
Page 62: ...62 NHB Service Manual Version 1 0 4 7 Ladder Diagram...
Page 142: ...142 NHB Service Manual Version 1 0 Memo...
Page 143: ...NHB Service Manual 143 Version 1 0 Memo...
Page 144: ...144 NHB Service Manual Version 1 0 Memo...
Page 145: ...NHB Service Manual 145 Version 1 0 Memo...