TOA Electronics P0055-DRG - Manual (Page 14)

14 NOTE: DIAGRAMS & ILLUSTRATIONS NOT TO SCALE.
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.
CORRECTIVE ACTION SYMPTOM
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
(thermopile) or remote wall
switch wiring.
B. Defective automatic valve
operator.
C. Defective limit switch.
A. Wall switch or wires
defective.
B. Pilot generator may not be
generating sufficient
millivoltage.
C. Plugged burner orifice.
A. Pilot flame may be too low or
blowing (high) causing the pilot
safety to drop out.
Check for spark at electrode and pilot; if no spark and electrode wire
is properly connected, replace the ignitor.
Using a match, light pilot. If pilot lights, turn off pilot and trigger the
red 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"
(3 mm) to have a strong spark. If gap measures ¹⁄₈", replace pilot
assembly (Figure 11 on page 7).
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 pilot generator (Figure 11 on
page 7). Clean and/or adjust pilot for maximum flame impingement
on generator.
Be sure wire connections from generator at gas valve terminals are
tight and generator is fully inserted into the pilot bracket.
One of the wall switch wires may be grounded. Remove wall switch
wires from valve terminals. If pilot now stays lit, trace wall switch
wires for a ground. May be grounded to appliance or gas supply.
With pilot operating (lit), check pilot generator with a millivolt meter.
Take reading at generator terminals of gas valve. Should read 325
millivolts minimum while holding valve knob depressed in pilot
position and wall switch “OFF.” Replace faulty generator if reading
is below specified minimum.
Turn knob to “ON,” place wall switch to “ON.” Millivolt meter should
read greater than 100mV. If reading is OK and the burner does not
come on, replace the gas valve.
Reset the limit switch button. If still not working, 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 defective and must be replaced.
Check wall switch and wires for proper connections. Place jumper
wires across terminals at wall switch. If burner comes on, replace
defective wall switch. If OK, place jumper wires across wall switch
wires at gas valve. If burner comes on, wires are defective or
connections are bad.
Re-check Symptom #2.
Check burner orifice for blockage and remove.
Clean/adjust pilot flame for maximum impingement on pilot genera-
tor
(Figure 11 on page 7).
POSSIBLE CAUSES
1. Spark ignitor will not
light pilot after repeated
triggering of red button.
2. Pilot will not stay lit
after carefully following
lighting instructions.
3. Pilot burning, no gas to
burner, valve knob “ON,”
wall switch “ON.”
4. Frequent pilot outage
problem.