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LENNOX HEARTH PRODUCTS • MERIT PLUS
®
DIRECT VENT GAS FIREPLACES (MPD33/35/40/45) • CARE AND OPERATION INSTRUCTIONS
TROUBLESHOOTING GUIDE: MILLIVOLT GAS CONTROL SYSTEM
Note: Before troubleshooting the gas control system, make sure the external gas shut off valve (located at gas supply inlet) is in the
“ON” position.
Note: Valve system troubleshooting should only be performed by a qualifi ed service technician.
1. Spark igniter will not light
pilot after repeated triggering
of igniter 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 ACTIONSYMPTOM
A. Defective igniter
(no spark at electrode).
B. Defective or misaligned electrode
at pilot (spark at electrode).
C. Gas supply pressure errant.
D. Pilot orifi ce plugged.
A. Defective pilot generator
(thermocouple).
A. Wall switch or wires defective.
B. Thermopile may not be generating
suffi cient millivoltage.
C. Plugged burner orifi ce.
A. Pilot fl ame 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 igniter.
POSSIBLE CAUSES
Clean and/or adjust pilot fl ame for maximum fl ame impinge-
ment on thermocouple (Figure 14 on page 17).
Check burner orifi ce for stoppage and remove.
Check thermopile with millivolt meter. Take reading at thermo-
pile terminals of gas valve. Should read 325 millivolts minimum
with optional wall switch “OFF.” Replace faulty thermopile if
reading is below specifi ed minimum.
Check wall switch and wires for proper connections. Jumper
wire across terminals at wall switch, if burner comes on, re-
place 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 pilot fl ame, it must impinge on thermocouple (Figure
14 on page 17). Clean and/or adjust pilot for maximum fl ame
impingement on thermocouple. Ensure that the connection
between the valve and thermocouple are tight and secure.
Clean or replace pilot orifi ce.
Check inlet gas pressure. It should be within the limits as
marked on the rating plate.
Using a match, light pilot. If pilot lights, turn off pilot and trig-
ger 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 – should be 1/8 in. to have a strong spark. If gap
measures 1/8 in., replace pilot (Figure 14 on page 17).
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