15
NOTE: DIAGRAMS & ILLUSTRATIONS ARE NOT TO SCALE.
LENNOX MERIT
®
SERIES B-VENT GAS FIREPLACES • 36" LMBV MODELS • CARE AND OPERATION INSTRUCTIONS
TROUBLESHOOTING THE MILLIVOLT GAS CONTROL SYSTEM
1.
Spark ignitor will not light
pilot after repeated triggering
of ignitor button.
2.
Pilot will not stay lit after
carefully following the light-
ing instructions.
3.
Pilot burning, no gas to
burner, Valve knob “ON,”
Wall Switch “ON.”
4.
Frequent pilot/burner outage
problem.
CORRECTIvE ACTION
SymPTOm
A.
Defective ignitor
(no spark at electrode).
b.
Defective or misaligned electrode
at pilot (spark at electrode).
C.
Gas supply pressure errant.
D.
Pilot orifice plugged.
A.
Defective pilot generator (thermo-
generator).
A.
Damper closed or Damper Switch
defective.
b.
Wall switch or wires defective.
C.
Thermopile may not be generating
sufficient millivoltage.
D.
Plugged burner orifice.
A.
Pilot flame may be too low or
blowing (high) causing the pilot/
valve safety to drop out.
Check for spark at electrode and pilot; if no spark and electrode
wire is properly connected, replace ignitor.
Using a match, light pilot. If pilot lights, turn off pilot and
trigger the ignitor button again. If pilot lights, an improper
gas mixture caused the bad lighting and a longer purge
period is recommended. If pilot will not light – check gap at
electrode and pilot - should be 1/8" to have a strong spark.
If gap measures 1/8", replace pilot (Figure 9
).
Check inlet gas pressure. It should be within the limits as
marked on the rating plate.
Clean or replace pilot orifice.
Check pilot flame, it must impinge on thermogenerator (Figure
9 ). Clean and/or adjust pilot for maximum flame impingement
on thermogenerator. Ensure that the connection between the
valve and thermogenerator are tight and secure.
Ensure damper control lever is locked in the open position,
all the way to the right. If the damper control lever is locked
in the open position troubleshoot through Steps B., C. and D.
below. If the main burner will still not light, determine if the
damper switch is defective and replace if necessary.
Check wall switch and wires for proper connections. Jumper
wire across terminals at wall switch, if burner comes on,
replace defective wall switch. If okay, jumper wires across
wall switch wires at valve, if burner comes on, wires are faulty
or connections are bad.
Check thermopile with millivolt meter. Take reading at ther-
mopile terminals of gas valve. Should read 325 millivolts
minimum with optional wall switch “OFF.” Replace faulty
thermopile if reading is below specified minimum.
Check burner orifice for stoppage and remove.
Clean and/or adjust pilot flame for maximum flame impinge-
ment on thermogenerator (Figure 9 ).
POSSIblE CAUSES
Note: Before troubleshooting the gas control system, be sure external gas shut off valve (located at gas supply inlet) is in
the “ON” position.
Important: Valve system troubleshooting should only be accomplished by a qualified service technician.
