Gas Furnace - Gas Fires then Shuts Off

Article ID: 159
Last updated: 11 Jan, 2019

Gas Furnace

Re: Burners Fire then Shut Off

The furnace goes through a normal ignition sequence, but several seconds after ignition the burners shut off.

Qty Possible Causes:
3 Dirty flame sensor
Bad Ignition Control
Incomplete Ignition
Pressure Switch Opening
Thermostat Short-Cycling


1. Check Power to Ignition Control

  • Check for 24VAC power between "TH" or "24V" on ignition control and "C" on the terminal block.
  • Monitor power through the ignition sequence.
    • Power drops out when burners shut off = Pressure Switch Opening or Thermostat Short-Cycling
    • Power stays on but burners shut off β†’ Step 2. Check Ignition

2. Check Ignition

  • Visually inspect the burners during ignition.
    • Burners should light with little or no delay from the glow plug to the flame sensor.
      • Make sure flame sensor comes in good contact with the flame.
      • Any delay or burners not igniting = Clogged Burners
      • Burners light properly β†’  Step 3. Check Flame Sensor

3. Check Flame Sensor

  • On the multi-meter:
    • Switch the test leads to "COM" and "mA".
    • Set the meter on DC 200ΓΉ.
    • 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.
      • Minimum acceptable reading = 1 MicroAmp
        • Low Reading β‡’ Clean Flame Sensor & Re-check
        • Normal Reading (2 to 6 mA) but Shuts Off = Bad Ignition Control

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Article ID: 159
Last updated: 11 Jan, 2019
Revision: 13
Access: Public
Views: 64
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