Service Manual

69
Service Procedure II:
Combustion System Testing and Replacement (Continued)
Observe burner operation through the sight glass located on the combustion insert mounting flange. Normal
burner operation should ignite smoothly, without evidence of coughing or huffing upon ignition. The burner
flame should be a blue flame near the burner surface in a uniform flame pattern. Occasional yellow or white
streaks are normal. Note: On this high input model that uses metal fiber mesh burner a red glow from
the burner surface is normal.
Continued from page 68.
Refer to the control board
illustration. Is there 24 VAC
between brown and blue wires
coming out of the control harness
during the flame establishing
period? Note: Control display must
show “Heating” for operating status.
Check to see brown
and blue wires are
properly connected
to molex connectors
on control harness.
Make connections.
Replace control.
Can you hear or feel the gas valve energize?
Replace gas valve harness and/or gas valve
(see Gas Valve Replacement Procedure, pg 74).
Does the burner light smoothly, without
evidence of coughing or huffing?
Does the burner stay lit?
Check flame sensor. Are there
at least 1-5 micro amps (min.)
during 1.5 second flame
proving period? Value may be
displayed on the control display
by accessing Service Mode.
Check for obstruction at
inlet of gas valve. Is inlet
free of obstruction?
Clear obstruction. If there is no
obstruction, inspect the burner tube
(see Burner Tube Inspection, pg 73).
Does the burner operate
normally until the
thermostat is satisfied?
System O.K.
Replace
flame sensor
(see Flame
Sensor
Replacement
Procedure,
pg 78).
Call Technical Support.
N
N
N
N
N
N
N
N
Y
Y
Y
Y
Y
Y
Y
Y
Gas Valve/Venturi
Inlet pressure
tap
Flame sense
terminal
Flame sense
rod
Multimeter set to
microamp (µA)
setting
WARNING
120 volt potential exposure. Use caution making
voltage checks to avoid personal injury.
69