Navien NP-180 Service Manual page 127

Whirring
Low gas pressure
(whirring)
Noise from burner
stage switch
Noise during
combustion
©Navien America Inc. 2010
Exhaust gas flow into the boiler through the air inlet makes
combustion noise.
Check the distance between inlet and outlet (at least 6").
Check the distance between flues if two or more units are installed
(at least 24").
Check if there is any obstacle near the flue.
1. Noise occurs due to flame lifting when gas pressure is low.
Check the gas supply pressure (dynamic pressure)
2. Low gas supply due to differential pressure error.
Set DIP S/W 1, 2 to ON (3-stage MIN),
3. Noise due to clogged or damaged gas pressure sensor hose.
4. Check the failure of the gas pressure sensor (output voltage check).
Disassemble the nozzle and check if the hole is narrowed due to
foreign substance.
Set DIP S/W 1, 2 to ON (3-stage MIN), and check the flame.
Compare flame of Burner at combustion section of stages 1, 2 and 3.
Check the nozzle if there is a comparatively unbalanced burner
section.
Noise due to defective air pressure sensor.
Replace the air pressure sensor.
Noise due to torn air pressure hose.
Noise may be intermittent depending on the size of the damage.
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NR/NP series service Manual Version 2.0