YP9C - Flashing Code 7

Article ID: 553
Last updated: 23 Jan, 2023

York Gas Furnace: YP9C / PC9

Re: Flashing Code 7

Code 7 = Failure to Sense Flame (3 attempts)

► If flame cannot be established in three tries, the control will lockout for one hour and then automatically try again to light.

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


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 ramps-up to close the pressure switch.
    • 2. The inducer motor ramps-down to open the pressure switch.
    • 3. The inducer motor ramps-up to close the pressure switch again.
    • 4. The control board powers the glow plug.
    • 5. The gas valve should open within 20 seconds of the glow plug energizing.

2. 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
  • Re-connect the glow plug and 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 + No Glow = Bad Glow Plug

3. Check Ignition

  • Visually inspect the burners during ignition.

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 Inlet Gas Pressure:
      • 5" w.c. for Natural Gas
      • 11" w.c. for LP or 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.
    • No Gas Pressure = Bad Gas Valve
    • Proper Gas Pressure + No or Delayed Ignition = Clogged Burners Remove burners and clean spreaders
    • No Gas Pressure = Bad Gas Valve
    • Low Gas Pressure ⇒ Check Hi-Fire gas pressure 
      • ONLY ADJUST MANIFOLD PRESSURE AT HI-FIRE! See Test Mode article for instructions to force Hi-Fire.

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 = 3.7 mA
      • Low Level Warning = 1.5 mA
      • Lockout Point = 0.1 mA
        • Low Reading = Dirty Flame SensorClean Flame Sensor & Re-check
    • CAUTION! Move meter leads back to "COM" and "V" before proceeding!

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Article ID: 553
Last updated: 23 Jan, 2023
Revision: 17
Access: Public
Views: 215
Comments: 0