Troubleshooting The Millivolt Gas Control System - Lennox Hearth Products MPLDV-30NM Care And Operation Instructions Manual

TROUBLESHOOTING THE MILLIVOLT GAS CONTROL SYSTEM

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.
SYMPTOM
1. Spark ignitor will not light
pilot after repeated
triggering of ignitor button.
2. Pilot will not stay lit after
carefully following the
lighting instructions.
3. Pilot burning, no gas to
burner, Valve knob "ON,"
Wall Switch "ON."
4. Frequent pilot/burner outage
problem.
16
POSSIBLE CAUSES
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
(thermocouple).
A. Wall switch or wires defective.
B. Thermopile may not be generating
sufficient millivoltage.
C. Plugged burner orifice.
A. Pilot flame may be too low or
blowing (high) causing the pilot/
valve safety to drop out.
NOTE: DIAGRAMS & ILLUSTRATIONS NOT TO SCALE.
CORRECTIVE ACTION
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 8 on page 8 ).
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 ( Figure
8 on page 8) Clean and/or adjust pilot for maximum flame
impingement on thermocouple. Ensure that the connection
between the valve and thermocouple are tight and secure.
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 thermo-
pile terminals of gas valve. Should read 325 millivolts mini-
mum with optional wall switch "OFF." Replace faulty thermo-
pile 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 thermocouple ( Figure 8 on page 8 ).