26
NOTE: DIAGRAMS & ILLUSTRATIONS ARE NOT TO SCALE.
LENNOX HEARTH PRODUCTS • MERIT PLUS
®
DIRECT VENT GAS FIREPLACES (MPD33/35/40/45) • INSTALLATION INSTRUCTIONS
TEST ALL CONNECTIONS FOR GAS LEAKS
(FACTORY ANd FIELd)
Pilot
Hood
Sensor
Ignitor
Igniter
Flame Rod
(sensor)
Pilot Hood
Step 8. VERIFYING APPLIANCE OPERA-
TION
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 Instruc-
tions
. 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 first 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 flame (remove logs, if neces-
sary, handling carefully)
WARNING
Never use an open flame to
check for leaks.
Turn on gas supply and test for gas leaks, us-
ing a gas leak test solution (also referred to as
bubble leak solution).
NOTE:
Using a soapy water solution is an effec-
tive leak test solution but it is not recommended,
because the soap residue that is left on the
pipes/fittings 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.
Electronic Appliance Checkout
To light the burner, turn ‘ON’ the wall or remote
control switch. Ensure the igniter lights the pilot.
The pilot flame should engulf the flame 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
Millivolt Appliance Checkout
The pilot flame should be steady, not lifting
or floating. Flame should be blue in color with
traces of orange at the outer edge.
The top 3/8" (10 mm) at the pilot generator
(thermopile) and the top 1/8" minimum (tip)
of the quick drop out thermocouple should be
engulfed in the pilot flame.
The flame should project 1" (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).
Thermocouple
Hood Igniter Rod
Thermopile
Pilot
Nozzels
3/8”
(9 mm)
Min
