SERVICE PROCEDURE D24-IIIMain Burner Operation Testing
CAUTION
Be Careful When Making Voltage
Measurements or Jumping Terminals
Not to Damage orDeform Connectors or
Connector Pins.
DANGER
120 volt exposure. To avoid personal injury,
use caution while performing this procedure.
Condition:
Main burner will not light,
Display shows“Heating” undertemperature
setpoint.
Tank is cold.
Is Pilotlit? See “Pilot Will Not
Light”
Does control boardcontinue to spark with
pilot lit?
See “Pilot Lights, No Flam e
Signal”
Insert meter probes int o back of
“Control” plugon control board to contact
pins for measuring voltage.
Is there 22-27 volts AC across
pinterminals 5 & 8? (Refer to wiring
diagram also see photo 14)
Disconnect brown wire lea d from
“MV” terminal of gas valve.
Is there 22-27 volts AC across
brown wire lead & ground?
(see photo 15)
Replace control board.
Be sure control displa y is showing “Heati ng”,
pilot is lit and controlis not sparking.
Recheck voltage across c ontrol board
pin terminals 5 & 8 (MV & MV/PV)
Is voltage present?
Check wire harness for d amage or loose
connections.Repair or replaceas needed.
Check incoming gas pressure
to gas valve and manifold
pressureto burners (See next
page for procedure for
checking manifold pressure).If
inlet gas pressure is O.K.,
replace gas valve. (See ph oto
on next page for gas valve
inlet pressure tap)
N
Y
NN
Y
N
Y
Y
N
Y
Checking MV &
MV/PV control plug
pins to gas valve
for 24 volts output
during heating
cycle (pilotmust be
lit withno
sparking).
Brown wire disconnected
from“MV ” terminal of gas
valve
Ground lug of
gas valve
Checking mainvalve (MV) voltage to gas valve.
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