Troubleshooting Guide: Millivolt Gas Control System - Lennox Hearth Products MPB33 Care And Operation Instructions Manual

LENNOX HEARTH PRODUCTS • MERIT PLUS

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.
SYMPTOM
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.
Pilot will not stay lit
after following the
lighting instructions.
Pilot burning, no gas
to burner, valve knob
ON, wall switch ON.
Frequent pilot/burner
outage problem.
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B-VENT GAS FIREPLACES (MPB33/35/40/45) • CARE AND OPERATION INSTRUCTIONS
®
POSSIBLE CAUSES
Defective igniter (no spark at electrode).
Defective or misaligned electrode at pilot (spark
at electrode).
Gas supply pressure errant.
Pilot orifice plugged.
Defective pilot generator (thermocouple).
Limit Switch defective.
Wall switch or wires defective.
Thermopile may not be generating sufficient
millivolts.
Plugged burner orifice.
ON/OFF Switch and *Remote Switch are in the
ON position resulting in excessive resistance.
Pilot flame may be too low or blowing (high)
causing the pilot/valve safety to drop out.
CORRECTIVE ACTION
Check for spark at electrode and pilot; if no spark and electrode wire is
properly connected, replace Igniter.
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).
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 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.
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.
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 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.
Check burner orifice for stoppage and remove.
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.
Clean and/or adjust pilot flame for maximum flame impingement on
thermocouple (see Figure 16 on Page 18).