Having an electronic ignition furnace that won’t light can be extremely frustrating, especially when you need heat. Thankfully, there are several troubleshooting steps you can take to get your furnace working again.
Why Your Electronic Ignition Furnace Won’t Light
There are a few common reasons why your electronic ignition furnace fails to ignite:
Faulty Ignitor
The ignitor is responsible for sparking and lighting the gas burner. Over time, the ignitor can wear out or fail. Visual inspect the ignitor to look for cracks or damage. Use a multimeter to check for continuity. Replace the ignitor if faulty.
Dirty Flame Sensor
The flame sensor monitors the burner to ensure the gas is igniting properly. If the sensor gets dirty, it can fail to detect the flame and shut off the gas valve. Carefully clean the flame sensor with steel wool or fine sandpaper.
Faulty Gas Valve
The gas valve is what allows gas to flow to the burner. If it fails to open, no gas will reach the burner. Use a multimeter to test for voltage at the gas valve. If present, the valve could be stuck or faulty and need replacement.
No Power
If there is no power to the furnace, the ignitor cannot activate to light the gas. Check the furnace circuit breaker or fuse. Inspect all wiring connections. Restore power if needed.
No Gas
The burner cannot ignite if gas is not reaching it. Confirm the gas supply line is turned on and inspect the line for leaks. Contact the gas company if shutdown.
Blown Fuse
Some electronic ignition furnaces have an internal fuse that burns out over time. Locate and visually inspect the fuse, replacing it if faulty.
Faulty Control Board
The control board regulates voltage to ignition system components. Use a multimeter to test for 24-120VAC. If voltage is absent, the board could be defective and need replacement.
Step-by-Step Troubleshooting Guide
Follow these steps to methodically troubleshoot and fix an electronic ignition furnace that fails to light:
1. Verify Power Supply
Start by verifying the furnace has power:
- Check the furnace circuit breaker or fuse at the main electrical panel. Reset or replace if tripped/blown.
- Inspect the power switch on the side of the furnace. Flip to OFF and back ON.
- Check for 120VAC power at the line voltage terminal block. If no power, trace wiring back to source.
- Inspect all wiring connections to ignitor, gas valve, and control board. Reconnect any loose wires.
2. Check for Gas Supply
Next, confirm gas is reaching the unit:
- Verify the main gas line shut-off valve is in the ON position.
- Check the manual gas valve on the gas supply pipe to the furnace. Lever should be parallel to pipe.
- Inspect the gas supply line for leaks using bubble solution. Tighten any fittings leaking gas.
- Contact the gas company if gas supply is interrupted to the property.
3. Test the Hot Surface Ignitor
The ignitor heating up is what ignites the gas. Test as follows:
- Turn OFF power and remove the ignitor wire from the control board.
- Reapply power and use a multimeter to check for 120VAC at the board connection. If no voltage, the board could be bad.
- Inspect the ignitor visually – look for cracks or damage. Replace if defective.
- With power OFF, check ignitor resistance with a multimeter. Look for 40-75 ohms at room temp and under 1 ohm when hot. Replace if outside these values.
4. Check Flame Sensor
The flame sensor verifies a flame is present. Test it:
- Turn off power and disconnect the sensor wire from the control board.
- Turn power back on and check for 5VDC at the board connection using a multimeter. If no voltage, the board could be faulty.
- Clean the sensor gently with fine steel wool or sandpaper. Do not bend the probe.
- Verify the sensor is secure in the burner flame. Position if needed. Replace sensor if visibly damaged.
5. Inspect Burners and Heat Exchangers
Look for blockages preventing gas flow or ignition:
- Remove burner access panel and inspect inside burners for any blockages.
- Clean burners using compressed air or a soft bristle brush. Vacuum debris.
- Check heat exchangers for cracks, rust, or separated seams.
- Ensure burner ports are all clear of dust, dirt, spider webs, etc.
6. Evaluate Gas Valve
The gas valve must open for gas to flow to the burners:
- Turn power OFF and disconnect wires from gas valve, including ground.
- Restore power and check for 24VAC at valve connections using a multimeter. If no voltage, the board could be faulty.
- Listen for an audible click when unit tries to ignite. If no click, the valve could be stuck.
- Use needle nose pliers to gently tap on the gas valve, freeing a stuck internal mechanism.
- Replace gas valve if still not opening. Match model numbers exactly.
7. Test Control Board Voltages
The control board distributes voltage to ignition components:
- Set multimeter to AC voltage and check for 24-120VAC at board terminals during ignition cycle.
- If voltages are absent, the board is likely defective and needs replacement. Match part numbers.
- Check for 5VDC at the flame sensor wire connection. If missing, the board is bad.
- Verify 120VAC power supply voltage is stable during ignition cycle.
8. Rule Out Blown Fuse
Some furnace control boards have an internal fuse:
- Locate fuse on the control board, typically near the power terminal screw.
- Remove fuse and inspect it visually for a broken filament.
- Use a multimeter on the Ohms setting to test fuse continuity.
- If fuse is blown, replace with a new one of the exact same size, voltage, and speed ratings.
9. Examine Wiring
Damaged or deteriorated wires can prevent proper operation:
- Inspect all wiring in the furnace for cracked, frayed, or broken wires.
- Check for loose wire connections at the control board and ignition components.
- Ensure wires are routed properly and not pinched or rubbing bare metal.
- Repair or replace any damaged wiring as needed.
10. Watch Ignition Sequence
Observe the unit attempting to ignite:
- Set the thermostat to call for heat and initiate the ignition sequence.
- Watch and listen for the ignitor heating up and sparking.
- Check that the gas valve clicks open. Audible fuel flow should occur.
- Confirm the burner ignites and the flame sensor detects it.
- If any part of the sequence fails, focus troubleshooting there.
When to Call a Professional
If you’ve worked through these troubleshooting steps and the furnace still fails to ignite, it’s best to call a professional service technician. A qualified pro will have advanced diagnostic tools to pinpoint any complex problems. They can also safely inspect heat exchangers and service gas valves. Paying for an expert repair is preferred over struggling with a serious HVAC issue or having an unsafe malfunctioning unit.
FAQs
What if the ignitor sparking but no flame?
- This indicates a fuel delivery issue. Check the gas valve operation and supply line. Inspect the burners for blockages. The orifices or heat exchangers could be dirty or damaged.
Why does the burner ignite briefly then shut off?
- If the burner lights briefly before shutting down, the flame sensor is likely dirty or faulty. Clean the sensor and verify 5VDC at the control board terminal. Replace sensor if needed.
The furnace keeps cycling on/off without heating right?
- Cycling without reaching the set temperature can be caused by a stuck closed gas valve, dirty filter, blower issue, or problem with the thermostat.
How can I test the gas valve on my furnace?
- Turn off power and disconnect the valve wires. Restore power and check for 24VAC at the terminals. Listen for click during ignition. Tap valve with pliers to free stuck internals. Replace if faulty.
What if I have no voltage to my electronic ignition board?
- Check for tripped breakers, blown fuses, and wiring issues. Inspect connections at the terminal block. Test the transformer for proper secondary voltage. The circuit board may need to be replaced.
Conclusion
Troubleshooting an electronic ignition furnace that fails to light involves methodically inspecting components like the ignitor, flame sensor, gas valve, and control board. Check for proper voltage at each part, clean or replace faulty ones, and verify gas flow. With attention to detail, you can often resolve ignition issues without a costly service call. But for complex or safety-related problems, rely on the expertise of a professional furnace technician.