Service Manual

74
Service Procedure II
Combustion System Testing and Replacement
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 higher input models using metal fiber
mesh burner a red glow from the burner surface
is normal.
WARNING
120 volt potential exposure. Use caution making
voltage checks to avoid personal injury.
WARNING
Removing screw from inlet gas pressure tap will
immediately allow gas to flow from pressure tap.
Verify minimum gas supply piping requirements of: Minimum
¾" NPT (Schedule 40 black iron pipe recommended).
Venturi
Inlet gas
pressure
With manometer, check inlet gas
pressure. Is it stable between 7"
& 14" W.C. static? (heater not
running) (see images at right)
Is gas supply
pressure regulator
adjustable to
maintain a proper
and stable setting?
Does the inlet gas
pressuredrop more
than 2" W.C. during
burner ignition?
Inadequately
sized
regulator.
Adjust gas
supply regulator.
Can sparking be
seen/heard at the spark
rod to the burner?
Remove high voltage wire connected at the spark rod
and hold approximately ¼" from metal ground with
insulated pliers during the ignition cycle (3 second
spark trial period). Is there spark to ground?
Check resistance of high voltage cable. Resistance
should be 0-1 ohms. If resistance is high, replace spark
cable. If spark cable is good, replace the control board.
Does the main
burner light?
See next page.
Check spark gap to burner (see Spark
Rod Gap Inspection, pg 88).
Check the continuity of the spark
rod. Is the reading 0-1 Ohm?
Replace Spark Rod (see
Spark Rod Gap Inspection
and Replacement, pg 88).
N
N
N
N
N
N
Y
Y
Y
Y
Y
Y
N
CHECK SPARK ROD RESISTANCE
Meter probe
Meter probe
Spark rod
Volt meter set to
Ohm setting
Reconfigure
gas supply
piping.
Y
N
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