Heil Gas Furnace: NUGK

Re: Burners Won't Ignite

These furnaces use a Honeywell spark ignition control and universal electronic ignition (3-wire) gas valve.

• When the ignition control receives 24VAC on "TH" or "25V" it should start sparking through the ignition cable and send power out "PV" to open the Pilot Valve of the gas valve.
• Once pilot flame is sensed, the ignition control should send power out "MV" to open the Main Valve of the gas valve and ignite the burners.

► The ignition control only senses pilot flame, so any ignition faults will be related to the pilot flame only.

CHECKOUT

1. Check Power

• Check for 24VAC between "R" and "C" on the low voltage wiring.
  • Power Present → Step 2. Check Ignition Sequence
  • No Power ⇒ Check the Blower Door Switch and High Voltage Power to Furnace
    • High Voltage + No Low Voltage ⇒ Check Transformer

2. Check Ignition Sequence

• Set thermostat to call for Heat
• Check 24VAC between "W" and "C" on the low voltage wiring.
  • No Power = No Heat Call ⇒ Check Thermostat
  • Power + No Inducer = Bad Inducer or Bad System Relay
  • Inducer Running ⇒ Continue
• Check for 24VAC at the ignition control between "TH" or "25V" and "C".
  • Power Present → Step 4. Check Ignition Control
  • No Power or Power Drops-Out → Step 3. Check Safeties

3. Check Safeties

• With the thermostat calling for heat, check each of the following safeties:
• Inducer Limit (Vent Temp Switch)
• Check for 24VAC between each side of the limit switch and "C".
  • Power on Both Sides = Limit Switch Closed ⇒ Check Roll-Out Limit
  • Power on One Side Only = Limit Switch Open
• Roll-Out Limit
• Check for 24VAC between each side of the limit switch and "C".
  • Power on Both Sides = Limit Switch Closed ⇒ Check Primary Limit
  • Power on One Side Only = Limit Switch Open
• Primary Limit
• Check for 24VAC between each side of the limit switch and "C".
  • Power on Both Sides = Limit Switch Closed ⇒ Check System Relay
  • Power on One Side Only = Limit Switch Open
• System Relay (In the control panel)
• Check for 24VAC between Terminal 4 (BL) and "C".
  • Power Present = Relay Closed ⇒ Check Pressure Switch
  • No Power = Bad System Relay
• Pressure Switch
• Check for 24VAC between each side of the pressure switch and "C".
  • Power on Both Sides = Pressure Switch Closed
  • Power on One Side Only = Pressure Switch Open

4. Check Ignition Control

• Once 24VAC is present on "25V" or "TH" of the ignition control, the pilot should try to light.
  • Sparks but Does Not Light Pilot → Step 5. Check Gas Valve/Pilot
  • Pilot Lights but No Main Gas → Step 5. Check Gas Valve/Pilot
  • No Spark = Bad Ignition Control

5. Check Gas Valve Pilot

• Check for 24VAC between "PV" and "MV/PV" at the ignition control.
  • Power on "25V" + No Power on "PV" = Bad Ignition Control
  • Power Present ⇒ Continue
• Turn the gas valve to the "Off" position.
• Remove the pilot line from the gas valve and turn the valve back "On".
• Check for pilot gas leaving the gas valve.
  • Power on "PV" + No Pilot Gas = No Gas Supply or Bad Gas Valve
  • Pilot Gas Present ⇒ Re-attach pilot line, clean the pilot orifice and re-check.
• Make sure the pilot flame makes good contact with the flame sensor.
  • Little or No Contact = Increase Pilot Pressure
  • Good Contact + No Main Gas ⇒ Check for 24VAC between "MV" and "C".
    • No Power = Bad Ignition Control
    • Power + No Ignition = No or Low Gas Supply or Bad Gas Valve ⇒ Check Gas Pressure