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Radiance Direct Vent /Natural Vent Gas Heater
20004188
Troubleshooting / Honeywell #8420 Gas Control System
NOTE: Before troubleshooting the gas control system, be sure the external gas shutoff is in the “ON” position.
WARNING: REMOVE THE GLASS PANEL BEFORE PERFORMING ANY GAS CONTROL SERVICE WORK.
SYMPTOM
POSSIBLE CAUSES
CORRECTIVE ACTION
1. Spark ignitor will
not light
2. Pilot will not stay lit
after carefully fol-
lowing the lighting
instructions
3. Pilot lights, no gas
to burner, valve
knob ON, remote
switch (rocker
switch) ON
4. Frequent pilot out-
age
A. Defective or misaligned
electrode at the pilot
B. Defective ignitor (push but-
ton)
A. Defective pilot generator
(thermocouple)
B. Defective automatic valve
operator
A. Remote switch or wires
defective
B. Thermopile may not gener
-
ate sufficient voltage
C. Plugged burner orifice
D. Defective automatic valve
operator
A. Pilot flame may be too low
or high, (blowing or lifting),
causing the pilot to drop out
B. Possible blockage of the
vent terminal
Using a match, light pilot. If pilot lights, turn off pilot and
push the ignitor button again. If pilot will not light, check
gap at electrode and pilot - it should be 1/8” to have a
strong spark.
Push piezo ignitor button. Check for spark at electrode
and pilot. If there is no spark at the pilot, and electrode
wire is properly connected, replace ignitor.
Check pilot flame. It must impinge on the thermocouple
or thermopile. NOTE: This pilot burner assembly uses
both a thermocouple and a thermopile. The thermocou
-
ple operates the pilot flame. Tighten the thermocouple.
The thermopile operates the main valve (ON and OFF).
Clean and/or adjust pilot for maximum flame impinge-
ment on thermocouple and thermopile.
Turn valve knob to ‘Pilot’. Maintain flow to pilot; millivolt
meter should read greater than 10mV. If the reading
is okay and the pilot does not stay on, replace the gas
valve. NOTE: An interrupter block (not supplied) must be
used to conduct this test.
Check rocker switch and wires for proper connection.
Use jumper wires across terminals at rocker switch. If
burner lights, replace rocker switch. If okay, use jumper
wires across rocker switch wires at the valve; if burner
lights, wires are faulty or connections are bad.
1. Be sure wire connections from thermopile at gas valve
terminals are tight and thermopile is fully inserted into
pilot bracket.
2. One of the rocker switch wires may be grounded.
Remove rocker switch wires from valve terminals. If
burner now stays lit, trace rocker switch wiring from
ground. It may be grounded to the appliance or the
gas supply line.
3. Check the thermopile with a millivolt meter. Take read
-
ing at thermopile (“TP” and “TP/TH”) terminals of gas
valve. Should read 325 millivolts minimum while hold-
ing valve knob depressed in PILOT position and with
rocker switch OFF. Replace faulty thermopile if reading
is below specified minimum.
Check burner orifices for debris, and remove.
Turn knob to ON, place rocker switch to ON, millivolt me-
ter should read greater than 10 mV. If the reading is okay
and the burner does not light, replace the valve.
Clean and/or adjust pilot flame for maximum flame im-
pingement on thermocouple and thermopile.
Check the vent terminal for blockage.