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Note: Pump must be running during the
troubleshooting procedure.
These procedures require a voltmeter with a
minimum 0-1000 mVDC range. Figure 24 shows the
pilot generator and control circuits, and where to take
measurements. Location numbers and letters in circles
have been added, and will be referenced in the follow-
ing sections.
As stated at the beginning of this manual, some
of these procedures are hazardous. Only a qualified
service technician should service the heater.
During the trouble shooting procedure, the filter
pump must be on, the pilot on the heater must be lit,
the ON/OFF switch on the heater must be in the ON
position and the control knob must be turned to the
maximum setting so that there is a call for heat. We
recommend turning the gas valve control knob to the
"PILOT" position to prevent the main burners from
firing throughout the procedure. Before starting the
procedure, be sure that the pilot has been lit for at least
2 minutes and that the pilot generator (thermopile) is
positioned correctly within the flame of the pilot.
The pilot generator also operates the pilot coil of
the gas valve, allowing gas to flow to the pilot when
the gas valve knob is released from the pilot lighting
position (see Section 7.3 "Lighting and Shutdown
Procedures"). If the pilot will not stay lit when the gas
valve knob is released, check the pilot generator
output as described in Section 10.4.2 and replace if
necessary. If the pilot generator output is sufficient,
then check the gas valve as outlined in Section 10.4.1.
10.4.1
Gas Valve
The gas valve consists of two separate internal
operating valves. The main valve supplies gas to the
main burners for heater operation. The pilot valve
supplies gas to the pilot when the pilot generator
activates the pilot coil.
If the pilot will not stay lit after following the
lighting instructions in Section 7.3, check for the
following:
• Pilot generator output
• Correct type of gas supplied
• Correct gas supply pressure
• Air in the gas line
• Pilot coil wire connections clean and tight
If the pilot will not stay lit after checking the
items listed above, the pilot coil may be causing the
fault. Replace the gas valve.
If the main burners will not light after following
the lighting instructions in Section 7.3, check the
voltage reading between the PP terminal on the gas
valve (test point 1) and the TH terminal on the gas
valve (test point 17). If the meter shows less than
220mVDC then there is a problem with the pilot
generator, the sensors in the safety loop or the control
panel. Follow the trouble shooting procedure as
outlined in sections 10.4.2 through 10.4.7.
If the meter shows more than 220mVDC at test
point 17, then check for the following:
• Correct type of gas supplied
• Correct gas supply pressure
• Correct gas manifold pressure
• Correct orifice size
• Air in the gas line
If the main burners will not stay lit after check-
ing the items listed above, the gas valve may be
causing the fault. Replace the gas valve.
10.4.2 Pilot Generator
The pilot generator generates a 700-750mVDC
signal when heated by the pilot flame. When the pilot
generator is connected to the heater's control compo-
nents, there will be some voltage drop in the circuit so
that the measured voltage will be less than 750mVDC.
But the measured voltage should never be below
500mVDC when the ON/OFF switch is in the "OFF"
position or 220mVDC when the ON/OFF switch is in
the "ON" position.
With the pilot generator connected to the gas
valve and the ON/OFF switch in the OFF position,
place the red lead of the voltmeter on the PP terminal
(test point 1) of the gas valve. Place the black lead of
the meter on the PP/TH terminal (test point 2) of the
gas valve. The meter should show a minimum of
500mVDC. If the meter show less than 500mV, check
for partial shorts, loose or corroded connections or
partially broken wires between the pilot generator and
the gas valve.
If the wires and connections are sound, check the
pilot generator output. Disconnect the pilot generator
from the gas valve. The pilot will go out. Light the
pilot while pressing down on the gas valve control
knob. Continue holding the knob for at least one
minute. Immediately measure the voltage between the
two wires of the pilot generator. If the meter does not
show at least 700mV, replace the pilot generator.
10.4.3
Fusible Link
Check the voltage going to the safety circuit. Be
sure that the pilot generator is correctly wired to the
gas valve, the pilot is light and the control knob on the
gas valve is in the "PILOT" position. Leave the red
voltmeter lead in place at test point 1. Touch the
black lead of the meter to the terminal of the fusible
link where the white wire from the gas valve is
connected (test point 3).
