28
LENNOX HEARTH PRODUCTS • MERIT PLUS
®
B-VENT GAS FIREPLACES (MPB33/35/40/45) • CARE AND OPERATION INSTRUCTIONS
SYMPTOM
POSSIBLE CAUSES
CORRECTIVE ACTION
Spark igniter will not
light pilot after repeat-
ed pressing of igniter
button.
WARNING: if the pilot
will not light after 1
minute of attempt-
ing, wait for at least
5 minutes for gas to
clear before attempt-
ing again.
Defective igniter (no spark at electrode).
Check for spark at electrode and pilot; if no spark and electrode wire is
properly connected, replace Igniter.
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 (igniter rod) and pilot - should be 1/8" to
have a strong spark. If gap measures 1/8", replace pilot (see
Figure 16
on Page 18
)
.
Gas supply pressure errant.
Check inlet gas pressure. It should be within the limits as marked on
the rating plate.
Pilot orifice plugged.
Clean or replace pilot orifice.
Pilot will not stay lit
after following the
lighting instructions.
Defective pilot generator (thermocouple).
Check pilot flame, it must impinge on thermocouple (see
Figure 16 on
Page 18
)
. Clean and/or adjust pilot for maximum flame impingement
on thermocouple. Ensure that the connection between the valve and
thermocouple are tight and secure.
Pilot burning, no gas
to burner, valve knob
ON, wall switch ON.
Limit Switch defective.
Isolate the “limit” switch. Disconnect the wires from the
ON/OFF switch and the valve (label wires for reattachment). Test for
continuity with a multimeter. If continuity is not indicated, switch is de-
fective and must be replaced.
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.
Thermopile may not be generating sufficient
millivolts.
Check thermopile with millivolt meter. Take reading at thermopile ter-
minals of gas valve. Should read 325 millivolts minimum with optional
wall switch OFF. Replace faulty thermopile if reading is below specified
minimum.
Plugged burner orifice.
Check burner orifice for stoppage and remove.
ON/OFF 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
unit mounted (optional) ON/OFF 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.
Frequent pilot/burner
outage problem.
Pilot flame 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 16 on Page 18
)
.
TROUBLESHOOTING GUIDE: MILLIVOLT GAS CONTROL SYSTEM
NOTE: Before troubleshooting the gas control system, Ensure external gas shut off valve, located at gas supply inlet, (and wall switch, if
applicable), is in the ON position.
NOTE: Valve system troubleshooting should only be performed by a qualified service technician.
