Service Procedure Ii: Combustion System Testing And Replacement - Bradford White UCG100H3993N Service Manual

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 this high input model that uses metal fiber mesh burner a red glow from the burner surface is normal.
Verify minimum gas supply piping requirements of: Minimum ¾" NPT
(Schedule 40 black iron pipe recommended.)
Y
With manometer, check inlet gas
pressure. Is it stable between 7" &
14" W.C. static (heater not
running)? (See illustrations at right.)
Y
Does inlet gas
pressure drop more
than 2" W.C. during
burner ignition?"
N
gas
valve/venturi
Can sparking be
seen/heard at the
spark rod to burner?
WARNING
120 volt potential exposure.
Y
Use caution making voltage
checks to avoid personal injury.
Y
Does main burner light?
Y
Proceed to next page.
Service Procedure II:
Inadequately
sized regulator.
N
Is gas supply pressure
regulator adjustable to
maintain proper and
stable setting?
Y
Inlet
Pressure
inlet gas pressure tap will
Tap
immediately allow gas to
N
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?
Y
Check continuity of
spark rod. Is
reading 0-1 Ohm?
N
Check spark gap to
burner (see "Spark Rod
Gap Inspection").
Reconfigure gas supply piping
N
Adjust gas
supply regulator.
N
Y
WARNING
Removing screw from
flow from pressure tap.
Replace spark rod (see
"Spark Rod Gap Inspection
N
and Replacement").
Volt meter set
of OHM setting
21
Volt meter set
Spark
to OHM setting
rod
Check resistance of high
N
voltage cable. Resistance
should be 0-1 Ohm. If
resistance is high, replace
spark cable. If spark cable is
good, replace control board.
Meter probe
Spark
rod
Meter probe
CHECK SPARK
ROD RESISTANCE
21