Heil Gas Furnace: NULK
Re: Burners Won't Ignite
These furnaces use a Hot-Surface ignition control for ignition (GHAC replacement = IGN.02).
Qty |
Possible Causes: |
1 |
Bad Ignitor |
|
Bad Gas Valve |
|
Pressure Switch Open |
1 |
Rollout Limit Tripped |
|
Bad System Relay |
|
Bad Primary Limit |
|
Blower Door Switch |
CHECKOUT:
1. Check Power
- Check for 24VAC between "R" and "C" on the terminal block.
- No Power ⇒ Check Blower Door Switch and High Voltage Power to Furnace
- High Voltage + No Low Voltage ⇒ Check the transformer.
- Energize a call for Heat from the thermostat
- Check 24VAC between "W" and "C" on the terminal block.
- No Power = No Heat Call, check the thermostat.
- Ensure that the inducer motor starts.
- Power + No Inducer = Bad Inducer or Bad System Relay
- Inducer Running ⇒ Check for 24VAC between "TH" on the ignition control and "C" on the terminal block.
2. Check Safeties
- Roll-Out Limit
- Mounted above the burners, Typically a manual-reset limit.
- Check for 24VAC between both sides of the limit (Red wires) and "C" on the terminal block.
- Power on One Side Only = Limit Tripped ⇒ Push Reset button & Re-check
- Primary Limit
- Check for 24VAC between each Red wire of the limit to "C" on the terminal block.
- Power on One Side Only = Bad Limit or Limit Tripped
- Open Limit + Cold Heat Exchanger = Bad Limit
- Open Limit + Hot Heat Exchanger ⇒ Suspect Blower Problem
- System Relay
- Check for 24VAC between terminals 4 (Blue) and 6 (Red) of the System Relay to "C" on the terminal block.
- Power on One Side Only = Bad System Relay
- Pressure Switch
- Check for 24VAC between each wire on the pressure switch (Blue wires) & "C" on the terminal block.
- No Power = Bad System Relay
- Power on One Side Only = Pressure Switch Open
3. Check Ignition Control
- Look for a flashing lockout light on the control.
- Flashing Light = Lockout ⇒ Reset power and retry.
- The Glow plug should begin glowing within 30 seconds of receiving power on "TH".
- Gas Valve should energize within 60 seconds of powering the glow plug.
4. Check Glow Plug
- Look for any visual cracks.
- Use a meter to test resistance of glow plug.
- No Resistance = Bad Glow Plug
- Check for 120V power to the Glow Plug during an ignition sequence.
- No Power = Bad Ignition Control
- Power Present + No Glow = Bad Glow Plug