Navien NCB-24LSWE, Service Manual

Page: 94 / 144

92 NCB Service Manual Version 1.0
Testing method
Fault Possible causes Testing method
Flame loss and
noise occurs
after ignition
Low gas supply
pressure
1. Check the gas supply pressure.

NG: 17 - 25 mbar, LP: 25 – 35 mbar

LP pressure drop occurs frequently during winter.
2. When static pressure is normal, the use of other gas appliances may cause the
boiler’s gas pressure to drop. Check the dynamic pressure.
Check the static pressure: Gas supply pressure in standby mode.
Check the dynamic pressure: Gas supply pressure at maximum combustion.
3. Check the gas pipe connections.

If a CSST connector has been used, ensure that it has not been
overtightened. An overtight connection can deform the seal and obstruct
the flow of gas.
4. Check the gas meter rating.
Flame loss and
noise occurs
after ignition
PCB DIP switch
setting errors
Check the PCB DIP switch settings.
Switch Function Settings
1 & 2
Gas type
selection
G20 (LNG) 1-OFF, 2-OFF
G25, G27 (LNG) 1-OFF, 2-ON
G30 (LPG) 1-ON, 2-OFF
G31 (LPG) 1-ON, 2-ON
Offset pressure
adjustment error
Low fire (Stage 1- minimum) offset adjustment error

From the front panel to set the unit at "MIN.1" (refer to page 55).

Open the offset pressure port on the gas valve and connect a manometer. Use
the positive pressure side on a dual port manometer.

If the pressure is outside of the range, adjust the offset pressure by turning the
adjustment screw on the gas valve with a 4 mm (5/32" )Allen wrench.