Gas Furnace

Re: Check Flame Sensor

• If furnace is running, de-energize the call for heat and allow the furnace to cool.
• Turn off power to the furnace.
• Remove the wire that plugs into the top of the flame sensor.
  • On some models the flame sensor lead is hard-wired to the flame sensor, which requires unplugging the wire at the ignition control.
• Use a multi-meter to read the flame signal:
  • Switch the test leads to "COM" and "mA".
  • Set the meter on DC 200ù.
  • Place one meter lead on the flame sensor terminal and the other on the flame sensor wire.
    • It is helpful to have an "alligator" clip on the lead attached to the flame sensor.
• Re-establish power to the furnace.
• Initiate a call for heat from the thermostat or by placing a jumper between "R" and "W".
• When the burners ignite, check the micro-amp reading on the multi-meter.
  • Normal reading = 2 to 6 mA
  • Minimum acceptable reading = 1 MicroAmp
    • No Reading ⇒ May have a blown meter fuse
    • Low Reading ⇒ Clean Flame Sensor & Re-check
    • Normal Reading but still shuts-off = Bad Ignition Control
• MOVE SENSOR LEADS BACK TO "COM" and "V" BEFORE PROCEEDING!
• REMOVE THE JUMPER WIRE IF USED TO START HEAT!