Lochinvar EW150 Installation & Service Manual page 28

3
Gas connections
Figure 3-4 Gas Manifold Pressure Adjustment
10. Remove the 1/8" hex plug, located on the "outlet" side
of the gas valve and install a fitting suitable to connect
to a manometer or magnahelic gauge (see FIG. 3-4).
Minimum range of scale should be up to 5" w.c. for
natural gas and 10" w.c. for propane gas.
11. A reference pressure hose is factory installed from the
barbed connection on the gas valve regulator to the
fan pressurized front chamber. All manifold pressure
measurements made with the reference hose in place
will be the sum of the net manifold pressure and the air
pressure in the front chamber.
12. Turn the power switch to the "ON" position.
13. Turn all gas valve knobs to the "ON" position.
14. Set the thermostat to call for heat.
15. Before the valve opens, the manometer or magnahelic
gauge will read a positive air pressure of 1.4" w.c. to 1.8"
w.c. in the jacket as supplied by the combustion air fan
in the prepurge cycle. There is no gas flow at this point.
This air pressure reading is normal.
16. The gas valve will open at the end of the trial for
ignition stage and remain open as the burners fire.
Observe the gas manifold pressure when valves open. If
insufficient gas pressure is supplied to the burners, the
burners will not fire. Record the gas pressure indicated
on the manometer or magnahelic. Subtract the air
pressure in the front chamber (as recorded in Step 6)
from the gross manifold pressure observed at the end
of trial for ignition and when the burners are firing.
28
Installation & Service Manual
The gross manifold pressure will typically be within
the range of 3.4" w.c. to 3.9" w.c. for Natural Gas
and 6.1" w.c. to 6.7" w.c. for L.P. Gas at full fire. The
difference in the gross manifold pressure and the front
chamber pressure is the net manifold pressure setting
of the gas valve's regulator. Compare the net setting to
the setting specified for the type of gas used. Adjust
regulator as required. Set the thermostat to a setting
lower than the appliance's water temperature to turn
the burners off. Allow appliance to run through the
post purge sequence. Turn the power switch to the
"OFF" position.
TABLE 3F
NET MANIFOLD PRESSURE
REGULATOR SETTING
LESS FRONT CHAMBER
Type of Gas
Natural Gas
LP Gas
The front chamber pressure must be
NOTE
subtracted from the gross regulator
pressure to obtain actual net manifold
pressure for normal operation. The
front chamber pressure may vary based
on elevation, stages of operation, vent
length and model. For information on
chamber pressure, see Combustion
Air Adjustment. Do NOT increase net
manifold pressure beyond the specified
pressure setting.
17. If adjustment is necessary, remove the regulator cover
screw on the gas valve.
18. Turn regulator adjustment screw clockwise to raise
regulator gas pressure, counterclockwise to lower the
regulator gas pressure. Turn regulator adjustment screw
1/4 turn in the desired rotation and cycle the burners on
in the sequence listed below and record the observed
chamber and regulator settings. Subtract to determine
the net manifold pressure setting. Repeat as necessary
to achieve the specified net manifold pressure setting.
19. Replace cover screw on the regulator and turn the
power switch to the "ON" position. Set the thermostat
to call for heat. Observe gas regulator pressure again at
the burner "ON" stages. Repeat this sequence until the
proper regulator setting has been obtained.
Net Manifold
Pressure Setting
1.8" w.c.
4.6" w.c.