DNH - Pilot Lights but Burners Won't Ignite

York Package Units: DNH

Re: Pilot Lights but Burners Won't Ignite

These package gas/electric units use a Honeywell Smart Valve for ignition.

• Sequence Of Operation
• On a call for heat, the fan timer board starts the inducer fan motor and sends 24V through the pressure switch to the Smart Valve.
• When the Smart Valve receives a demand for heat it powers the 24V glow plug and opens the pilot valve.
• When a pilot flame is sensed, the Smart Valve opens the main valve to allow gas flow to the burners.

CHECKOUT:

1. Check Pilot Flame

• Observe the pilot flame to ensure that it comes into steady contact with the flame sensor.
  • Steady Contact + No Main Flame → Step 4: Check Flame Sensor
  • Little or No Contact → Step 2. Check Gas Pressure

2. Check Gas Pressure

• Disconnect line voltage power from the unit.
• Shut the gas safety shut-off valve to the unit.
• Hook-up a gas pressure gauge to the inlet gas pressure port.
• Open the gas safety shut-off valve & monitor inlet gas pressure.
  • No or Very Low Pressure = Gas Supply Issue
• Re-apply power to the unit.
• Energize a call for heat.
• Monitor inlet pressure while the glow plug energizes.
  • Inlet Pressure Drops Below Normal = Gas Supply Issue
  • Inlet Pressure OK → Step 3. Check Pilot Orifice

3. Check Pilot Orifice

• Disconnect the aluminum pilot tubing from the gas valve.
• Energize a call for heat.
• Ensure that gas comes out of the pilot gas port.
  • No Pilot Gas = Bad Smart Valve
  • Pilot Gas Present ⇒ Disconnect and blow through the pilot tubing to see if the pilot orifice is clear.
    • Pilot Orifice Clear ⇒ Increase Pilot Gas Pressure

4. Check Flame Sensor

• Disconnect the pilot tubing from the gas valve (if not already disconnected).
• Remove the two screws that mount the pilot assembly to the burner manifold.
• Carefully remove the pilot assembly along with the pilot tubing.
• Clean the flame sensor. BE CAREFUL NOT TO BREAK THE GLOW PLUG!
• Re-install the pilot assembly and re-connect the pilot tubing.
• Energize a call for heat.
• Ensure that the pilot lights and the main burners ignite.
  • Pilot + No Main Gas = Bad Smart Valve
  • Pilot + Main Gas + No Main Flame = Clogged Burners ⇒ Remove burners and clean burner wings.