StepExpected Result/Action
4. Shut off power to the unit. At the main burner enclosure, locate the wire
connected to the flame sensor electrode (FSE). Refer to the unit wiring and
parts location diagrams.
Power to unit is turned off and wire connected to the flame sensing electrode is
5. Set up a microammeter to measure DC current on the lowest microamp
range. Note that the current level expected can be between 0.5 to 4.5
Disconnect the lead from the flame sensor electrode, then connect the
microammeter in series with the flame sensor electrode and the wire
disconnected from the electrode as shown in Figure SP-11-5.
Microammeter connected in series with flame sensor electrode output and flameproving
circuit wire in preparation for measurement.
6. Turn on power to the unit and adjust the thermostat to call for heat. After the
unit has run for about 1 minute, observe the current indication on the
microammeter and compare it to the manufacturer's specifications.
The microammeter indicates a minimum DC current of 0.5 microamperes or a
value stated in the manufacturer's specifications. This indicates that a good
flame-proving signal is being generated.
If a flame-proving signal is low or not being generated, check for the following
• Check flame sensor rod position.
• Make sure the furnace is properly grounded per the manufacturer's
instructions. -----
• Make sure that the gas valve is grounded through the gas valve ground wire.
• Make sure that a good electrical contact exists at the flame sensor electrode
connection. ____
• Check flame sensor electrode for an oxide film coating. Clean with fine
If a flame-proving signal is not being generated and none of the conditions listed
above are the cause of the problem, refer to the manufacturer's instructions for
information about the operating sequence of events in the furnace and related
troubleshooting information.

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