Navien NPN Installation & Operation Manual page 25

2. Open a hot water faucet. The water heater
should turn on and the gas in the gas supply
line will be purged.
3. Leave the faucet on until the water heater shuts
down due to a lack of gas supply, and then turn
off the hot water faucet.
4. Remove the two upper screws from the
front cover assembly using a Phillips head
screwdriver. Then, release the toggle latch from
the bottom of the front cover assembly to gain
access to the internal components.
24 Installing the Water Heater
5. Remove the screw from the gas inlet fitting and
connect a manometer to the pressure port.
Reset the manometer to zero before use.
Digital pressure
manometer
6. Re-open the manual gas valve and check for
leaks.
7. Open multiple fixtures that have high flow rates,
such as bathtub and shower faucets, to ramp
the water heater up to its maximum firing rate.
8. When the water heater reaches its maximum
firing rate, check the inlet gas pressure reading
on the manometer. The gas pressure must fall
within the ranges specified on page 23.