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SERVICE
WARNING
Fire or Explosion Hazard
Attempted disassembly or repair can cause
property damage, severe injury or death.
Do not disassemble the gas valve; it contains no
replaceable components.
CAUTION
Equipment Damage.
Can burn out heat anticipator in thermostat.
Do not apply a jumper across (or short) the valve
coil terminals even temporarily.
If Main Burner Does Not Come On With
Call For Heat
1. Confirm that the gas control knob is in the ON
position.
2. Adjust the thermostat several degrees above the
room temperature.
3. Use a dc voltmeter to measure the voltage across
the THTP and TP terminals.
4. If no voltage is present, check the control circuit for
proper operation.
5. If proper control system voltage is present, replace
the gas valve.
WARNING TO THE APPLIANCE
OWNER.
For Your Safety, Read Before Lighting
Appliance.
WARNING
Fire or Explosion Hazard.
Can cause property damage, severe injury or
death.
Exactly follow the instructions for Pre-Lighting
Checks.
Test
Test Title
A
Coil Resistance
B
Thermopile
C
Thermocouple
D
Operator Pull-In
E
Resistance System
1.
Coil Resistance: Have thermostat contacts open
and Pilotstat know turned to OFF. If coil resistance
exceeds 3.6 ohms, replace valve.
Table 2. VS8420 Troubleshooting Table.
Connect Multimeter
Between Terminals
TP and TH
Open
TP and TPTH
Open
Tip
Open
TH and TP
Open
—
Closed
VS8420 MILLIVOLT GAS VALVE
Pre-Lighting Checks
1. Before lighting, smell around the appliance area for
gas. If the appliance uses LP gas, be sure to smell
next to the floor because LP gas is heavier than air.
2. If you smell gas, immediately shut off the manual
valve in the gas piping to the appliance or, on LP, at
the tank. Leave the building immediately and call
your gas supplier. If your gas supplier cannot be
reached, call the fire department.
3. Do not force the gas valve control knob. Use only
your hand to turn the control knob.
4. If the knob does not operate by hand, the valve
should be replaced by a qualified service techni-
cian.
5. The gas valve must be replaced if it was flooded
with water. Call a qualified service technician.
6. The gas valve is a safety device. It must be
replaced in the event of any physical damage such
as bent terminals, missing or broken parts, stripped
threads, or evidence of exposure to heat.
IMPORTANT
Follow the operating instructions provided by
the manufacturer of your heating appliance.
TROUBLESHOOTING GUIDE
WARNING
Fire or Explosion Hazard.
Can cause property damage, severe injury or
death.
Only a qualified service technician should
perform these troubleshooting procedures.
Use Fig. 8 and Table 2 as a troubleshooting guide for the
VS8420.
M17559
Fig. 8. Identification of VS8420 terminals
for troubleshooting.
Set Thermostat
Meter Reading Should Be
Maximum of 3.6 ohms.
Minimum of 460 mV.
Minimum of 18 mV.
Minimum of 155 mV.
Maximum of 1.7 Ohms.
2. Thermopile: Have thermostat contacts open and
the pilot lit with Pilotstat knob turned to PILOT. If
reading is less than 460 mV, replace thermopile.
7
WIRING TERMINALS
69-1165—3
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