Navien NCB300-28K, Service Manual

Page: 21 / 108

20 System Details
To measure the inlet gas pressure:
1. Shut off the manual gas valve on the gas supply line pipe.
Gas Valve
Opened Closed
2. Open a hot water tap. The boiler should turn on and the gas
in the gas supply line will be purged.
3. Leave the tap on until the boiler shuts down due to a lack of
gas supply, and then turn off the hot water tap.
4. Unfasten the two latches (at the top) and remove two
screws (at the bottom) to remove the front cover and gain
access to the internal components.
CAUTION
Ensure that no cables are in the way before folding down
the PCB assembly. If the assembly is stuck, do not force
it. Doing so may damage the cables and result in serious
malfunctions. Check again to ensure that no cables or any
other parts are in the way before you proceed.
4.2 Measuring the Incoming Gas Pressure
WARNING
The boiler cannot function properly without sufficient inlet
gas pressure. Measuring the inlet gas pressure should be
performed by a licensed professional only.
Natural Gas Connection
●
The gas supply must comply to the current Gas Safety
(Installation and Use) Regulations, in accordance with BS 6891.
●
The nominal inlet working gas pressure measured at the
appliance should be 21 mbar +/- 2 mbar for Natural gas (G20).
Allowing for the acceptable pressure loss of 1 mbar across
the installation pipework, it can be assumed that a minimum
permitted operating pressure of 18 mbar will be delivered
to the inlet of the appliance. (Reference BS 6400-1 Clause 6.2
Pressure Absorption).
●
When tested at the gas valve, the pressure drop from the
meter to the gas valve must not be more than 4 mbar.
Propane Gas Connection (LPG)
●
For use with propane gas, the LPG conversion kit has to be
installed, see separate conversion instructions.
●
The LPG installation must comply to the current Gas Safety
(Installation and Use) Regulations, in accordance with BS 6891.
●
Installing of a LPG installation should only be done by a
registered LPG installer.
●
The tank must be provided with a high pressure regulator with
a minimum capacity of 24 kg/h to reduce the tank pressure
from 5 to 1.5 bar. The 1.5 bar high pressure gas line should
have a minimum diameter of 15 mm. In the high pressure gas
line a house pressure regulator must be installed.
●
When tested at the gas valve, the pressure drop from the
pressure regulator to the gas valve must not be more than
2.5 mbar.
●
Each gas appliance which is connected to the propane
installation must be provided with its own house pressure
regulator. The house pressure regulator is a third party part.
The house pressure regulator must have a minimum capacity
of 10 kg/h/37 mbar and a CE certification.