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LENNOX HEARTH PRODUCTS • MERIT
®
SERIES B-VENT GAS FIREPLACES • MODELS MLBV-35, MLBV-40 • CARE AND OPERATION INSTRUCTIONS
SYMPTOM POSSIBLE CAUSES CORRECTIVE ACTION
1. Spark igniter will not light pilot after
repeated triggering of igniter button.
WARNING: if the pilot will not light
after 1 minute of lighting attempts,
wait at least 5 minutes for gas to
clear before attempting again.
A. Defective igniter (no spark at electrode). Check for spark at electrode and pilot; if no spark and
electrode wire is properly connected, replace igniter.
B. Defective or misaligned electrode at pilot
(spark at electrode).
Using a match, light pilot. If pilot lights, turn off pilot
and trigger the igniter 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; it should be
1/8" to have a strong spark.
C. Gas supply pressure errant. Check inlet gas pressure. It should be within the limits
as marked on the rating plate.
D. Pilot orifice plugged. Clean or replace pilot orifice.
2. Pilot will not stay lit after carefully
following the lighting instructions.
A. Defective pilot generator
(thermocouple).
Check pilot ame, it must impinge on thermocouple
(see Figure 14 on Page 16). Clean and/or adjust pilot
for maximum flame impingement on thermocouple.
Ensure that the connection between the valve and
thermocouple are tight and secure.
3. Pilot burning; no gas to burner;
valve knob set to “ON”; and
burner OFF/ON switch (unit-mounted
switch, wall switch, or remote
control) is set to “ON.”
A. Wall switch or wires defective. 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.
B. Thermopile may not be generating
sufficient millivolts.
Check thermopile with millivolt meter. Take reading at
thermopile terminals of gas valve. Should read 325
millivolts minimum with optional wall switch in the
“OFF” position. Replace faulty thermopile if reading
is below specified minimum.
C. Plugged burner orifice. Check burner orice for blockage; remove, if found.
D. OFF/ON Switch and *Remote Switch are
in the ON position, resulting in excessive
resistance.
When turning on the burner using a *remote switch,
ensure that the standard OFF/ON switch is in the “OFF”
position. If both switches are in the “ON” position,
it may result in excessive resistance (and millivolt
drainage) and the burner may not come on.
4. Frequent pilot/burner outage
problem.
A. Pilot ame may be too low or blowing (high),
causing the pilot/valve safety to drop out.
Clean and/or adjust pilot flame for maximum flame
impingement on thermocouple (see Figure 14 on
Page 16).
TROUBLESHOOTING GUIDE – MILLIVOLT CONTROL SYSTEM
Note: Before troubleshooting the gas control system, make sure the external gas shut off valve (located at gas supply inlet)
and wall switch (if applicable) are in the “ON” position.
Important: Valve system troubleshooting should only be performed by a qualified service technician.