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V- SYSTEMS SERVICE CHECKS
A-Heating System Service Checks
All LGT units are ETL/CSA design certified without modifi
cation.
Before checking piping, check with gas company or author
ities having jurisdiction for local code requirements. Refer
to the LGT installation instruction for more information.
1-Gas Piping
Gas supply piping must not allow more than 0.5”W.C.
(124.3 Pa) drop in pressure between the gas meter and the
unit. Supply gas pipe must not be smaller than the unit gas
connection. Refer to installation instructions for details.
2-Testing Gas Piping
NOTE-In case emergency shutdown is required, turn off
the main manual shut‐off valve and disconnect the main
power to the unit. These controls should be properly la
beled by the installer.
When pressure testing gas lines, the gas valve must be dis
connected and isolated. Gas valves can be damaged if
subjected to more than 0.5 psig [14”W.C. (3481 Pa)].
See figure 25.
UNIT
GROUND
JOINT UNION
MANUAL MAIN
SHUT-OFF VALVE
(REFER TO LOCAL CODES)
GAS PIPING
SUPPORT
DRIP LEG
ROOF
MOUNTING
FRAME
GAS PIPING COMPONENTS
REFER TO INSTALLATION INSTRUCTIONS
VALVE
CAP HERE TO
ISOLATE VALVE
WHEN PRESSURE
TESTING LINE
FIGURE 25
When checking piping connection for gas leaks, use the
preferred means. Common kitchen detergents can cause
harmful corrosion on various metals used in gas piping.
The use of specialty Gas Leak Detector is strongly recom
mended.
Do not use matches, candles, flame or any other
source of ignition to check for gas leaks.
3-Testing Gas Supply Pressure
When testing gas supply pressure, connect test gauge to
the inlet pressure tap located on unit gas valve GV1 and or
GV3. Test supply gas pressure with unit firing at maximum
rate (both stages energized). Make sure the reading falls
within the range of the following values. Low pressure may
result in erratic operation or “underfire.” High pressure can
result in permanent damage to the gas valve or “overfire.”
For natural gas units, operating pressure at the unit gas
connection must be between 4.7”W.C. and 10.5”W.C.
(1168 Pa and 2610 Pa). For L.P. gas units, operating pres
sure at the unit gas connection must be between 10.8”W.C.
and 13.5”W.C. (2685.3 Pa and 3356.7 Pa).
On multiple unit installations, each unit should be checked
separately while operating at maximum rate, beginning
with the one closest to the supply gas main and progressing
to the one furthest from the main. Multiple units should also
be tested with and without the other units operating. Supply
pressure must fall within the range listed in the previous
paragraph.
4-Check and Adjust Manifold Pressure
After line pressure has been checked and adjusted, check
manifold pressure. Move test gauge to the outlet pressure
tap located on unit gas valve GV1 and or GV3. See figure
24 for location of pressure tap on the gas valve.
The manifold pressure is factory set and should not require
adjustment. If manifold pressure is incorrect and no other
source of improper manifold pressure can be found, the
valve must be replaced. See figure 24 for location of gas
valve (manifold pressure) adjustment screw.
All gas valves are factory regulated. The gas valve should
completely and immediately cycle off in the event of gas or
power failure. The manual shut‐off knob can be used to im
mediately shut off gas supply.
CAUTION
For safety, connect a shut‐off valve between the ma
nometer and the gas tap to permit shut off of gas
pressure to the manometer.
Manifold Adjustment Procedure
1- Connect test gauge to the outlet pressure tap on the
gas valve. Start the unit (call for second stage heat) and
allow five minutes for the unit to reach steady state.
2- While waiting for the unit to stabilize, notice the flame.
The flame should be stable without flashback and
should not lift from the burner heads. Natural gas
should burn basically blue with some clear streaks.
L.P. gas should burn mostly blue with some clear yel
low streaks.
3- After allowing the unit to stabilize for five minutes,
record the manifold pressure and compare to the val
ues given in table 7.
CAUTION
Disconnect heating demand as soon as an
accurate reading has been obtained.
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