Lennox International Inc. MERIT PLUS MPB3530CNM-B - Manual (Page 24)

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NOTE: DIAGRAMS & ILLUSTRATIONS ARE NOT TO SCALE.
LENNOX HEARTH PRODUCTS • MERIT PLUS ® B-VENT GAS FIREPLACES (MPB33/35/40/45) • INSTALLATION INSTRUCTIONS
Step 4. Carefully remove the logs. Exercise
care so as not to break the logs.
Step 5. Refer to Figures 26, 27, or 28.
A. Remove the grate and sub fl oor.
B. Remove the two (2) screws securing the
burner assembly.
C. Remove the burner assembly with
attached venturi tube.
MILLIVOLT AND ELECTRONIC IGNITION
SYSTEM APPLIANCES
Step 6. SIT Systems—Refer to Figure 37
and the instructions provided with the SIT
Regulator Conversion Kit. Using a Torx T20
driver to remove and discard the pressure
regulator mounting screws (two screws for
electronic models, three screws for millivolt
models), pressure regulator tower, the
diaphragm assembly (if applicable) and the
spring. Discard all removed components.
Step 7. Install the new pressure regulator
assembly using the supplied screws. Tighten
the screws with a torque of 25 lb-in.
Step 8. Install the enclosed identifi cation
label to the valve body where it can be easily
seen.
Step 9. Refer to Figure 38. Remove the
pilot hood assembly to access the hexed
pilot orifi ce. Remove and replace the orifi ce
with the one provided with the kit. Exercise
extreme care to prevent damage to or
breakage of the igniter assembly.
Figure 37: Regulator Conversion
Pressure
Regulator
Remove
These
Components
Electronic Valve
Millivolt Valve
Model
Series
Nat.Gas
drill size (inches)
Propane
drill size (inches)
MPB33
#47 (.0785") *
99K74 •
(.048")*
99K78 •
MPB35
#44 (.086") *
60J80 •
#55 (.052") *
19L52 •
MPB40
#38 (.102") *
99K76 •
(.0625") *
21L01 •
MPB45
#36 (.104") *
24M10 •
#52 (.0635") *
37G00 •
Table 11: Burner Orifi ce Sizes
Elevation 0–4500 ft
( 0–1372 m)
* Standard size installed at factory
• Part /Cat. Number
Figure 39: Orifi ce
Pilot
Orifice
Figure 38: Millivolt Pilot
Step 10. Remove the burner orifi ce from the
manifold and replace it with the one provided
in the kit. See Table 11 for orifi ce sizes for
natural and propane models. Figure 39
illustrates the orifi ce.
Use pipe joint compound or Tefl on tape on
all pipe fi ttings before installing (ensure
propane resistant compounds are used in
propane applications, do not use pipe joint
compounds on fl are fi ttings).
Step 11. Retrieve the burner and hold the
venturi tube above the orifi ce. Set the burner
assem bly into position and secure with the
two screws previously removed.
Step 12. Reassemble the remaining
components by reversing the procedures
outlined in the Steps 1–5.
Step 13. Attach the conversion label provided
in the conversion kit next to the rating plate
on the appliance.
Step 14. Turn on gas supply and test for gas
leaks (refer to Page 27).
Step 15. Reapply electrical power at the
circuit breaker.
Step 16. Relight the main burner. The
lighting instructions can be found on the
lighting label in the control compartment
or in the Care and Operation Manual
provided with the appliance. Verify proper
burner ignition and operation. See Burner
Adjustments and Burner Flame Appearance
on Page 19.
Step 17. Inspect the pilot system for proper
fl ame. The pilot fl ame should engulf the
fl ame sensor as shown in Figure 23 on
Page 14.
Step 18. Using a manometer, test the inlet
and manifold gas pressures (see Tables 3
and 4 on Page 4).
ALWAYS TEST PRESSURES WITH THE
REGULATOR CONTROL VALVE AT THE
HIGHEST SETTING.