9
NOTE: DIAGRAMS & ILLUSTRATIONS ARE NOT TO SCALE.
LENNOX HEARTH PRODUCTS • MERIT® SERIES B-VENT GAS FIREPLACES • MODELS MLBV-35, MLBV-40 • CARE AND OPERATION INSTRUCTIONS
Figure 4
Supply Gas
Inlet
Pressure-Tap
(Manifold)
Regulator
Mounting
Screw
Burner Stage
Terminal Gas
Outlet
To Burner
Ground (TP)
Pilot Stage
Terminal
Pilot Gas Outlet
Pressure-Tap
(Inlet)
PILOT
OUT
VENT
LO
TH
TP
TH
TP
HI
IN
IN
IMPORTANT: Do NOT assume your fire-
place has a complete supplemental com-
bustion air system, and do NOT operate
the Outside Air Control Lever unless you
have verified with your dealer or distribu-
tor that a complete system is in place.
The hand-operated outside air control lever is
located on the lower LEFT side of the fireplace
opening. See Figure 5.
To open the outside air shutter, open the bot-
tom control access panel, reach into the control
compartment, and pull the outside air control
lever all the way out. The outside air shutter
should be fully open when the fireplace is in use
and completely closed when the fireplace is not
being used. Closing it when not in use will greatly
reduce the amount of outside cold air entering
the dwelling through the fireplace.
Figure 5
WARNING
Do not operate the shutoff lever unless a complete outside com-bustion air system has been installed with your appliance.
LIGHTING AN ELECTRONIC APPLIANCE
DURING A POWER OUTAGE
1. Install (2) “D” batteries in battery holder.
2. Light the appliance according to the
instructions on Page 24.
3. Operate the appliance normally.
4. After power is restored, remove the
batteries.
Note: To prevent batteries from draining
prematurely, do NOT install batteries until
needed (e.g., during a power outage or
if operating the appliance solely with
batteries).
SIT Millivolt
Gas Control Valve
Variable Flame
Height Adjustment
Manifold Pressure
Port
Inlet
Pressure
Port
Main Gas Control Knob
H
I
L
O
W
TPTH TP TH
P
I
L
O
T
P
I
L
O
T
O
N
it
O
F
F
IN OUT
Gas Inlet
Terminals TPTH, TP and TH
Gas
Outlet
Variable Flame
Height Adjustment
Manifold Pressure
Port
Inlet
Pressure
Port
Main Gas Control Knob
H
I
L
O
W
TPTH TP TH
P
I
L
O
T
P
I
L
O
T
O
N
it
O
F
F
IN OUT
Gas Inlet
Terminals TPTH, TP and TH
Gas
Outlet
Figure 3
Dexen Electronic
Gas Control Valve
Left Side of
Lower Control Compartment
Securing
Screw
Removed
Outside Air Control
Lever pulled DOWN
(Air Shutter OPEN)
Outside Air Control
Lever pushed UP
(Air Shutter CLOSED)
Securing
Screw
Installed
IMPORTANT: Do NOT move Air Control
Lever if securing screw is installed
(or if not sure it was removed).

Appliance Controls

Operation of millivolt and electronic gas
control systems differs. Before lighting and
operating your appliance, determine whether
you have a millivolt or electronic appliance,
and then familiarize yourself with the location of
the Gas Control Valve and Gas Shut-Off Valve
on your specific appliance.
• For general control location, see Figure 1.
• For MILLIVOLT appliances, see Figure 3
for a detailed illustration of the SIT Millivolt
Gas Control Valve.
• For ELECTRONIC appliances, see Figure 4
for a detailed illustration of the Dexen
Electronic Gas Control Valve.

Lighting the Appliance

• Detailed MILLIVOLT appliance lighting
instructions are on Pages 22 and 23 and
also on the label attached to the gas
control valve.
• Detailed ELECTRONIC appliance lighting
instructions are on Pages 24 and 25
and also on the label attached to the
gas control valve. Also see “Lighting
an Electronic Appliance During a Power
Outage,” below.

ON/OFF Control

Available ON/OFF control options for both
MILLIVOLT and ELECTRONIC models include a
unit-mounted ON/OFF switch (shown in Figure
1), a wall switch, or a remote control system.
See the “Accessory Components” section in
this manual for details.
Note: To prevent excessive resistance in
burner circuit (which can cause burner op-
eration problems), wire only one burner
control switch to the valve.

Adjusting Flame Height

After lighting the appliance, rotate the Flame
Height Adjustment Knob to adjust the flame in
a variable range from “LOW” to “HI” (manual
adjustment only; no remote options).
• For MILLIVOLT appliances, see Figure 3.
• For ELECTRONIC appliances, see Figure 4.
CONTROLS FOR OPTIONAL OUTSIDE COMBUSTION AIR KIT
An optional outside combustion air system
may be used with these appliances to provide
supplemental combustion air from outside the
home during appliance operation. If used, the
outside combustion air kit must be installed
before the fireplace is framed and enclosed in
the finished wall.
The Outside Air Control Lever for this type of
system is standard on all models (see Figure
5); however, do NOT operate the Outside Air
Control Lever if the complete system is NOT
installed.
When a complete outside supplemental com-
bustion air system is installed, the installer will
remove the securing screw from the control
lever on the LEFT side of the fireplace opening
(see Figure 5).
If the securing screw has NOT been removed,
and you have reason to believe your fireplace
has a complete outside supplemental combus-
tion air system, contact your dealer or distribu-
tor to have your appliance inspected.