SERVICE PROCEDURE
D24-III
Main Burner Operation Testing
CAUTION
Be Careful When Making Voltage
Measurements or Jumping Terminals
Not to Damage or Deform 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” under temperature
setpoint.
Tank is cold.
Is Pilot lit?
See “Pilot Will Not
Light”
Does control board continue to spark with
pilot lit?
See “Pilot Lights, No Flame
Signal”
Insert meter probes into back of
“Control” plug on control board to contact
pins for measuring voltage.
Is there 22-27 volts AC across
pin terminals 5 & 8? (Refer to wiring
diagram also see photo 14)
Disconnect brown wire lead 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 display is showing “Heating”,
pilot is lit
and control
is not sparking.
Recheck voltage across control board
pin terminals 5 & 8 (MV & MV/PV)
Is voltage present?
Check wire harness for damage or loose
connections. Repair or replace as needed.
Check incoming gas pressure
to gas valve and manifold
pressure to burners (See next
p a g e f o r p r o c e d u r e f o r
checking manifold pressure). If
inlet gas pressure is O.K.,
replace gas valve. (See photo
on next page for gas valve
inlet pressure tap)
N
Y
N
N
Y
N
Y
Y
N
Y
Checking MV &
MV/PV control plug
pins to gas valve
for 24 volts output
during heating
cycle (pilot must be
lit with no
sparking).
Brown wire disconnected
from “MV” terminal of gas
valve
Ground lug of
gas valve
Checking main valve (MV) voltage to gas valve.
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