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TM9Y - Flashing Code 8

Article ID: 577
Last updated: 28 Mar, 2023

York Gas Furnace: TM9T/TM9Y

Re: No Heat - Flashing Code 8

Code 8 = Flame was established but later lost - 5 times.

► This is a Soft-Lockout which will automatically reset after 1 hour.

Qty Possible Causes:
4 Dirty Flame Sensor
1 Water in Inducer
Clogged Burners
No or Low Gas Pressure
Bad Gas Valve
Combustion Air Problem
Water in the Gas Line


CHECKOUT:

1. Check Ignition Sequence

  • If the furnace is running, turn the thermostat off and allow the furnace to 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 start with no difficulty.
    • 2. The pressure switch should close within a couple seconds of the inducer starting.
    • 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.

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.

3. Check Gas Pressure / Valve

  • Inlet Gas Pressure
  • Check the inlet gas pressure with the furnace off.
  • Minimum Pressure = 5" w.c. for Nat. gas, and 11" w.c. for propane.
    • Low Pressure = Bad Meter or Regulator
  • Monitor the inlet gas pressure as the furnace attempts to ignite.
    • Pressure Drops Below Minimum = Bad Meter/Regulator or Restricted Gas Line
  • Manifold Gas Pressure
  • The TM9Y uses a 2-stage gas valve. Make sure set the gas pressure at "High Fire".
  • Check the manifold pressure when the furnace attempts to ignite.
    • Normal Pressure = 3 - 3.5" w.c. for Nat. Gas, 9 - 11" w.c. for LP
      • No Gas Pressure = Bad Gas Valve
      • Low Gas Pressure ⇒ Increase Manifold Gas Pressure
      • Normal Gas Pressure + No or Delayed Ignition = Clogged Burners
  • Continue to monitor the manifold pressure throughout the burning process.
    • Fluctuating manifold pressure may indicate Water in the Gas Line

4. Check Flame Sensor

  • DC Voltage Method
    • Set the multi-meter to 20 VDC.
    • Find the two, round test ports of the right-side of the furnace control board marked, "FLAME CURRENT".
    • Check for DC volts across the two test ports when the furnace fires.
      • 1 DC Volt = 1 uA
  • Direct Micro Amp Reading
    • 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 uA
      • Low Flame Signal Warning = 1.5 MicroAmp
      • Lockout Point = 0.1 MicroAmp
        • Low Reading = Dirty Flame Sensor ⇒ Clean Flame Sensor & Re-check
      • CAUTION! Move meter leads back to "COM" and "V" before proceeding!

5. Monitor Burners

  • Allow the burners to operate.
  • If possible, monitor the burners throughout the heating sequence with the burner door in-place.
  • Watch for any fluttering of the burners.
    • Normal Burning with Door Off + Fluttering with Door On = Recycling Exhaust or Combustion Air Problem
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Article ID: 577
Last updated: 28 Mar, 2023
Revision: 7
Views: 198
Comments: 0