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NOTE: DIAGRAMS & ILLUSTRATIONS ARE NOT TO SCALE.
LENNOX HEARTH PRODUCTS • MERIT PLUS
®
DIRECT VENT GAS FIREPLACES (MPD33/35/40/45) • INSTALLATION INSTRUCTIONS
Step 8. VERIFYING APPLIANCE
OPERATION
With gas line installed, run initial system
checkout before closing up the front of the
unit. Follow the pilot lighting instructions
provided in the Care and Operation
Instructions. For piezo igniter location on
millivolt appliances, see Figure 48.
Note: Lighting Instructions are also found on
the literature tag tied to the gas piping next
to the gas valve. To access the tag, open the
lower control compartment door (Figure 48)
by pushing in simultaneously the left and
right top corners of the door (the door is
hinged at the bottom). Remove the bottom
compartment door by sliding the hinge
pin, located at the door’s left side, to the
right until it disengages from the left corner
post hole.
When fi rst lighting the appliance, it will take
a few minutes for the line to purge itself of
air. Once purging is complete, the pilot and
burner will light and operate as indicated
in the instruction manual. Subsequent
lighting of the appliance will not require such
purging. Inspect the pilot fl ame (remove logs,
if necessary, handling carefully).
Millivolt Appliance Checkout
TEST ALL CONNECTIONS FOR GAS LEAKS
(FACTORY AND FIELD)
Turn on gas supply and test for gas leaks,
using a gas leak test solution (also referred to
as bubble leak solution).
Note: Using a soapy water solution is an
effective leak test solution but it is not
recommended, because the soap residue
that is left on the pipes/fi ttings can result in
corrosion over time.
A. Light the appliance (refer to the
lighting instructions label in the control
compartment or in the Care and Operation
Instructions manual).
B. Brush all joints and connections with the
gas leak test solution to check for leaks. If
bubbles are formed, or gas odor is detected,
turn the gas control knob (off/pilot/on) to
the “OFF” position (millivolt units), or turn
the receiver or remote control to the “OFF”
position (electronic units). Either tighten or
refasten the leaking connection, then retest
as described above.
C. When the gas lines are tested and
leak free, be sure to rinse off the leak
testing solution.
Pilot
Hood
Sensor
Ignitor
Igniter
Flame Rod
(sensor)
Pilot Hood
Thermocouple
Hood Igniter Rod
Thermopile
Pilot
Nozzels
3/8 in.
(9 mm)
Min
The pilot fl ame should be steady, not lifting
or fl oating. Flame should be blue in color
with traces of orange at the outer edge.
The top 3/8 in. (10 mm) at the pilot generator
(thermopile) and the top 1/8 in. minimum
(tip) of the quick drop out thermocouple
should be engulfed in the pilot fl ame.
The fl ame should project 1 in. (25 mm)
beyond the hood at all three ports (see
Figure 49). Replace logs if removed for pilot
inspection.
To light the burner; turn “ON” the remote wall
switch and rotate the gas valve control knob
counterclockwise to the “ON” position (“ON”
will be at the top side of the valve).
Electronic Appliance Checkout
To light the burner, turn ‘ON’ the wall or
remote control switch. Ensure the igniter
lights the pilot. The pilot fl ame should engulf
the fl ame rod as shown in Figure 50.
Figure 49: Millivolt Pilot
Figure 47: Gas Connection
Gas
Stub
1/2" x 3/8" Flare
Shut-Off Valve
3/8" Flex Tubing
3/8" NPT x 3/8"
Flare Fitting
3/8" Nipple
3/8" Union
3/8" Close Nipple
3/8" Shut-Off Valve
1/2" x 3/8"
Reducer
Gas
Valve
Optional Gas Flex Line Connector
Figure 50: Electronic Pilot
Piezo
Door Latch
(Optional) Burner
ON/OFF Switch
Main Gas
Shut-Off Valve
Gas Valve
Figure 48: Millivolt Gas Valve—Lower Control Compartment
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