Lennox Hearth Products MPB-35, Care And Operation Instructions Manual

9

NOTE: DIAGRAMS & ILLUSTRATIONS ARE NOT TO SCALE.

LENNOX HEARTH PRODUCTS  •  MERIT PLUS

®

 B-VENT GAS FIREPLACES (MPB33/35/40/45)  •  CARE AND OPERATION INSTRUCTIONS

Figure 2 - SIT Millivolt Gas Valve

NOTE: The piezo igniter is located behind the lower access panel (see Figure 1).

Variable Flame Height Adjustment

All millivolt and electronic appliances are 

equipped with a variable gas control valve. 

Flame height for these models may be ad-

justed through a range between fixed low and 

high settings, alternately, while the appliance 

is in operation. 
Adjust the flame height as desired after light-

ing the appliance by rotating the HI/LO flame 

control knob located on the front of the valve 

(refer to 

Figures 2 and 3

).

Vent Operation Test

After appliance installation, perform this vent 

operation test to verify that proper venting 

conditions exist:

1. 

Place unit in its normally-operated con-

dition, with the glass enclosure panel in 

place. 

2. 

Close all doors and windows in the room. 

Turn on all exhaust fans in the building.

3. 

Light the appliance.

4. 

Wait fifteen (15) minutes.

5. 

To check for venting action, start by hold-

ing a smoke producing device within an 

inch of one side edge (not top or bottom 

edge) of the glass enclosure panel. The 

smoke should be drawn toward the edge 

of the glass enclosure. Continue the test 

by moving the smoke producing device 

along the entire length of both side edges 

of the glass door.

6. 

If the smoke is not drawn into the firebox, 

turn off the appliance and call a qualified 

service technician.

Resetting The Safety Limit Switch

This appliance is equipped with a manually 

resettable safety limit switch. Refer to 

Figure 4 on Page 10

 for its location. If, during 

appliance operation, the flame goes out (inde-

pendently of the burner ON/OFF wall switch), 

it may be due to a blocked vent. If this condi-

tion occurs, the safety limit switch will acti-

vate, causing the fireplace burner to shut off.
To reset the safety limit switch, perform the 

following steps.

NOTE: Allow the appliance to cool com-

pletely.

1. 

Remove the top louver panel.

2. 

Reset the safety limit switch by pushing 

the red reset button located between the 

wire terminals on the back of the switch 

(See 

Figure 4, Detail A

)

.

3. 

The appliance should then relight and re-

main lit.

NOTE: If the appliance does not relight, turn 

off the appliance and call for a qualified ser-

vice technician to replace the blocked vent 

safety limit switch.

4. 

Reinstall the top louver panel.

H I

LO

W

TPTH

TP

TH

PILO

T

PI

LO

T

ON

OFF

Hi/Lo Flame Control Knob

Manifold Pressure Port

Inlet Pressure Port

Main Gas

Control Knob

IN

OUT

Millivolt Appliances

To light millivolt appliances, refer to the detailed 

lighting instructions found on 

Page 24

. 

Millivolt 

appliance lighting instructions may also be 

found on the pull-out lighting instruction labels 

attached to the gas control valve

.

Millivolt units are not provided with any 

factory-installed controls; therefore, one of 

the optional control switches is required to 

operate the unit (ON/OFF wall switch, unit-

mountable ON/OFF switch, remote control). 

See “Accessories” in this manual for details.

Once the pilot is lit, use the switch or remote 

control to turn the appliance on or off.

Electronic Appliances

To light electronic appliances, refer to the 

detailed lighting instructions on 

Page 26

. 

Electronic appliance lighting instructions 

may also be found on the pull-out lighting 

instruction label attached to the gas control 

valve

. 

If your electronic appliance is equipped with an 

optional wall switch or remote control kit, the 

appliance main burner may be turned ON and 

OFF using the wall switch or remote control.

CPI switch located to the right of the gas valve 

switches the pilot from intermittent operation 

(pilot goes out when the fireplace is turned off) 

to continuous pilot mode. The rocker switch 

will not turn the burner on or off.

Orange Wire

(from DFC Wire 

Harness)

Main Gas Inlet

3/8" NPT

Green Wire

(from DFC Wire Harness)

Inlet (IN) Test Port

Manifold (OUT) Test Port

HI/LO Flame 

Control Knob

Yellow Ground Wire

(from DFC Wire Harness)

Figure 3 - SIT Electronic Gas Valve