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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 troubleshooting guides for the
VS8521.
Test
Test Title
A
Coil Resistance
B
Thermopile
C
Thermocouple
D
Operator Pull-In
E
Resistance System —
Procedure:
1. Test A (Coil Resistance): Have thermostat contacts
open and Pilotstat knob turned to OFF. If coil
resistance exceeds 3.6 ohms, replace the valve.
2. Test B (Thermopile): Have thermostat contacts
open and the pilot lit with Pilotstat knob turned to
PILOT. If the reading is less than 460 mV, replace
th thermopile.
3. Test C (Thermocouple): Have thermostat contacts
open and pilot lit with Pilotstat knob turned to
PILOT. Reading should be a minimum of 12 mV in
a new ODS pilot burner assembly. If the reading is
less than 12 mV, replace the ODS pilot burner
assembly. The power unit will hold in down to 3
mV. If the output of the thermocouple is less than 3
mV, replace the ODS pilot burner assembly.
Home and Building Control Home and Building Control
Honeywell
1985 Douglas Drive North
Golden Valley, MN 55422
69-1223—1 G.R. Rev. 12-00
Table 2. VS8521 Troubleshooting Table.
Connect Multimeter Between Terminals
TP and TH
TP and TPTH
Tip (and Ground)
TH and TP
Honeywell Limited-Honeywell Limitée
35 Dynamic Drive
Scarborough, Ontario
M1V 4Z9
M17511
Fig. 8. Identification of VS8521
terminals for troubleshooting.
Set Thermostat Meter Read Should Be
Open
Open
Open
Open
Closed
4. Test D (Operator Pull-In): have thermostat contacts
open and pilot lit with Pilotstat knob turned to
PILOT. Close the thermostat contacts. Operator
will pull in with a minimum of 155 mV. Operator
makes audible sound during pull-in. If pull-in does
not occur, replace the valve.
5. Test E (Resistance System): System resistance
from the remote switch or thermostat and lead
wires should not exceed 1.7 ohms. If resistance is
above 1.7 ohms, reduce the resistance.
Printed in U.S.A. on recycled
paper containing at least 10%
post-consumer paper fibers.
Maximum of 3.6 ohms.
Minimum of 460 mV.
Minimum of 12 mV.
Minimum of 155 mV.
Maximum of 1.7 ohms.
www.honeywell.com
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