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TUD/TDD - Flashing Code 2

Article ID: 236
Last updated: 9 Sep, 2024

Trane Gas Furnace: TUD/TDD

Re: No Heat - Code 2

Code 2 = 3 Failed Ignition Attempts


Qty Possible Causes:
1 Bad Glow Plug
Dirty Flame Sensor
Clogged Burners
No or Low Gas Pressure
Bad Gas Valve
Bad Ignition Control


CHECKOUT:

1. Check Ignition Sequence

  • If the furnace is currently in lockout, reset by cycling power.
  • 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 Glow Plug

  • Look for any visual cracks.
  • Unplug the 2-wire connector to the glow plug.
  • Use a meter to test resistance of the glow plug.
    • No Resistance = Bad Glow Plug
  • Start an ignition sequence.
  • Check for 120VAC power on the 2-wire plug feeding the glow plug during an ignition sequence.
    • No Power = Bad Ignition Control
    • Power Present but No Glow = Bad Glow Plug

► Replacement Glow Plug --> Use GLO.03 (025-32625-000)


4. Check Gas Pressure / Valve

  • Inlet Gas Pressure
  • Turn off power to the furnace and close the gas safety shut-off valve.
  • Hook-up a gas pressure gauge to the inlet test port of the gas valve.
  • Open the gas safety shut-off and check 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 = Bad Meter/Regulator or Restricted Gas Line
  • Manifold Gas Pressure
  • Turn off power to the furnace and close the gas safety shut-off.
  • Move the gas pressure gauge to the manifold (leaving) test port on the gas valve.
    • CAUTION! Be sure to put the plug back in the inlet test port before proceeding!
  • Open the gas safety shut-off valve and re-apply furnace power.
  • Activate a call for heat and monitor the manifold gas pressure during an ignition attempt.
    • 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 but No or Delayed Ignition = Clogged Burners --> Remove burners and clean spreaders

5. Check Flame Sensor

  • 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 = 2 to 6 mA
      • 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!
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Article ID: 236
Last updated: 9 Sep, 2024
Revision: 10
Access: Public
Views: 57
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