DNQ - Won't Ignite / Code 5

Package Unit: DNQ

Re: Won't Ignite / Code 5

The sparker ignites the pilot but never senses flame to energize the main gas valve, and the control board shows no fault codes.

• The DNQ package unit has two control boards, an Ignition Control Board (ICB) and a CFM Control Board (CFMCB).
• The thermostat connections are on the CFM Board which controls the cooling and indoor blower.
• The CFM board sends heating outputs to the Ignition Control Board for all heating functions.

CODE 5 = 5 Consecutive Loss of Flame - The flame sensor detects the presence of pilot flame. Flame is not detected in 5 consecutive ignition attempts.

CHECKOUT:

1. Check Gas Pressure

• Use a gas pressure gauge to check the inlet gas pressure at the gas valve.
  • Low Inlet Gas Pressure = Gas Supply Problem

2. Check Ignition Sequence

• Energize a call for heat from the thermostat, or place a jumper between "R" and "W" on the CFM Board.
• Ensure that the inducer motor starts and the ICB sparks at the pilot.
  • No Inducer or No Spark ⇒ Check board for fault indications.
• Confirm that the inlet gas pressure maintains at the proper pressure.
  • Inlet Gas Pressure Drops = Gas Supply Problems
• Visually inspect the pilot to see if the pilot lights.
  • Pilot Doesn't Light ⇒ Check for 24VAC between "C" and "P" at the gas valve.
    • No Voltage = Bad ICB
    • Voltage + No Pilot = Bad Gas Valve or Clogged Pilot Orfice
• Visually inspect the pilot flame to make sure it comes into steady contact with the Flame Sensor.
  • No Contact = Low Pilot Pressure or Dirty Pilot Orifice
  • Contact but No Main Flame ⇒ Check for 24VAC between "C" and "M" at the gas valve.
    • Power + No Flame = Bad Gas Valve
    • No Power = Dirty Flame Sensor or Bad ICB ⇒ Clean the Flame Sensor and Recheck