York Gas Furnace: TM9M / YM9M / YP9C

Re: Flashing Code 8

Code 8 = Loss of flame signal

► Flame was established and later lost, 5 times during a heating cycle.

CHECKOUT:

1. Check Ignition Sequence

• If the furnace is running, turn the thermostat off and allow the furnace to shut-down & cool and the blower to stop operating.
• Initiate a call for heat from the thermostat and monitor the ignition sequence.
  • 1. The inducer motor should ramp up, down, then back up.
  • 2. The pressure switch should prove inducer operation.
  • 3. The glow plug should energize within 30 seconds of the pressure switch closing.
  • 4. The gas valve should open within 20 seconds of the glow plug energizing.
  • 5. After proving initial flame, the inducer and gas valve should drop to minimum fire rate.

2. Check Ignition

• Visually inspect the burners during ignition.
  • The burners should light smoothly with little or no delay from the glow plug to the flame sensor.
  • Make sure the flame sensor comes in good contact with the flame.
    • Burners Ignite Properly → Step 4.  Check Flame Sensor
    • Any Delay or Burners Not Igniting = Clogged Burners, Low Gas Pressure or Bad Gas Valve → Step 3.  Check Gas Pressure / Valve

3. Check Gas Pressure / Valve

• Inlet Gas Pressure
• Check the gas valve incoming gas pressure.
  • Minimum Pressure = 5" w.c. for Nat. gas, and 11" w.c. for propane.
  • Low Pressure = Bad Meter or Regulator
• Re-apply power to the furnace and activate a call for heat.
• Make sure the inlet gas pressure stays above minimum when the gas valve energizes.
  • Pressure Drops Below Minimum = Gas Supply Issue
  • Normal Gas Pressure but No or Delayed Ignition = Clogged Burners or Bad Gas Valve ⇒ Remove burners and clean spreaders then re-try.

4. Check Flame Sensor

• Monitor the flame signal through ignition, minimum fire and ramp-up.
• Method 1: Flame Sensor MicroAmp
• On the multi-meter:
  • Switch the test leads to "COM" and "mA".
  • Set the meter on DC 200ù.
  • Disconnect the wire from the flame sensor.
  • Place one meter lead on the flame sensor terminal and the other on the flame sensor wire.
  • Check the reading when the burners ignite.
    • Normal Reading = 3.7 MicroAmps
    • Minimum acceptable reading = 1 MicroAmp
      • Low Reading = Dirty Flame Sensor ⇒ Clean Flame Sensor & Re-check
  • CAUTION! Move meter leads back to "COM" and "V" before proceeding!
• Method 2: Control Board DC Voltage
• On the multi-meter:
  • Set the meter on DC Volts.
  • Check DC voltage at the control board "Flame Voltage" test points when the burners ignite.
    • 1 DC Volt = 1 MicroAmp