York Gas Furnace: PUDD

Re: Burners Cycling Off / Burners Won't Stay On

The furnace burners fire and run for several minutes, then the burners shut off and the furnace goes through another ignition sequence.

CHECKOUT:

1. Check for Power at LTB

• Check for 24VAC between "R" and "C" on the transformer terminal block.
  • No Power = Check Blower Door Switch and High Voltage Power to Furnace
  • High Voltage but no Low Voltage -->Check transformer.
• Monitor 24VAC power between "W" and "C" on the transformer terminal block.
  • No Power = No Heat Call from Thermostat --> Recheck Stat
  • Power drops out when burners kick-off = Thermostat Cycling
  • Power present when burners kick-off --> Step 2. Check for Power at Controller

2. Check for Power at Controller

• White-Rodgers - Check for 24VAC between "TH" and "TR".
• Robertshaw - Check for 24VAC between "24V" and "COM".
• IGN.02 - Check for 24VAC between "TH-W" and "24V (Gnd)".
  • Monitor voltage as the furnace operates.
    • Power drops out when burners kick-off = Safety Trip --> Step 3. Check Safeties
    • Power present when burners kick-off = Loss of Flame Signal --> Step 4. Check Flame Sensor

3. Check Safeties

• 1LP Pressure Switch (3-wire)
  • Check for 24VAC between "C" on the pressure switch (Red) & "C" on the terminal block.
    • Power drops out when burners kick-off = Pressure Switch Trip
    • Power present when burners kick-off --> Check 2LP Pressure Switch
• 2LP Pressure Switch (2-wire)
  • Check for 24VAC between "NC" on the pressure switch (Brn) & "C" on the terminal block.
    • Power drops out when burners kick-off = Pressure Switch Trip --> Check Furnace Drain
• Primary Limit
  • Check for 24VAC between the (Brn) wire of the limit to "C" on the terminal block.
    • Power drops out when burners kick-off = Limit Switch Trip
    • Power present when burners kick-off --> Step 4. Check Flame Sensor

4. 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.
    • Minimum acceptable reading = 1 MicroAmp
      • Low Reading --> Clean Flame Sensor & Re-check
      • Normal Reading (2 to 6 mA) but Shuts Off = Bad Ignition Control
  • MOVE SENSOR LEADS BACK TO "COM" and "V" BEFORE PROCEEDING!