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1.10.2 Troubleshooting the 24 VAC Circuit in Units with Interface Boards
Verify that the drain
valve is fully closed, then
turn the controller on.
Which LEDs are lit?
24V LED onlyNone
GV LED (with
or without
other LEDs)
Is 24VAC
present on IFB 24V
terminals?
Probable cause
is a failed 24-volt
transformer.
No
Is 24VAC
present on J1
Pin 6?
Yes
Probable cause
is a failed interface
board.
No
Is pilot lit?
Is 24VAC
present on Pin 20 of 20-pin
terminal block?
Is 24VAC
present at the gas
valve?
Yes
Yes
Yes
Attempt to light pilot. If
the pilot will not light, see
Troubleshooting the Gas
Valve on Page 1-33.
No
If unit has a drain safety switch,
probable cause is open or failed
switch. If not, probable cause is loose
or missing jumper between Pins 10
and 19 of 20-pin terminal block.
No
Probable cause is failed
wiring between 20-pin
terminal block and gas
valve.
No
Problem is with gas valve.
See Troubleshooting the
Gas Valve on Page 1-33.
Yes