Does your gas furnace continuously shut down after each startup and stop responding within a few minutes? If you answered yes, your gas furnace is likely in ignition lockout and will require a proper reset or additional repair work.
It can happen from simple things like a dirty flame sensor, clogged filter, or minor gas supply fluctuations to bigger issues like gas leaks or faulty heat exchangers. Ignoring this problem can lead to major potential risks including carbon monoxide poisoning and detonation.
In this article, I’m going to share about ignition lockout to help you understand, diagnose, and fix the issue.
What is Furnace Ignition Lockout?
Furnace Ignition lockout is a safety feature that shuts down a furnace when it fails to ignite after a few tries.
Modern furnaces have different safety features. Among them, there are several sensors to keep the unit in check to function properly. When one of these sensors detects an anomaly, the furnace controllers force a shutdown. After a few repeated attempts, the gas furnace goes into lockout.
This is usually good to prevent damage and maintain safety. This is why the furnace ignition lockout is necessary:
- Preventing gas buildup
- Avoiding carbon monoxide poisoning
- Protecting furnace components
- Ensuring safe operation
Common Causes of Furnace Ignition Lockout
To fix any issues properly it is important to point out what is causing the problem. The furnace ignition lockout happens when the furnace’s safety mechanisms detect a problem that prevents safe and reliable ignition. The detected problem can vary from dirty air filter to faulty control board.
Here are some common causes behind furnace ignition lockout:
1. Flame Sensor Issues
The flame sensor is a metal rod that sits in the burner’s flame and detects the presence of a flame. If there is a flame, the rod creates a current. The sensor picks up the current and signals the control board that the ignition is successful.
Here is how the flame sensor can send a wrong signal:
- Soot and carbon deposits accumulate on the rod and prevent it from sensing the flame.
- If it is not positioned properly or moved from its actual position for some reason, it won’t detect the flame.
- The sensor can fail altogether and send incorrect results.
When the flame sensor can detect the flame properly, the control board interprets it as a failed ignition. The control board then turns off the gas valve to stop any gas buildup. After multiple occurrences, you end up with a furnace ignition lockout.
2. Faulty Igniter
The igniter ignites the gas in the burners. Igniters can either heat up to a very high temperature or create a spark to burn the gas. The common igniter problems that can cause malfunctions are:
- Weakening or breaking from usage
- Wiring issues preventing the igniter from receiving power
When the igniter doesn’t work properly, it can’t light the gas. As a result, the burner flame doesn’t light up in the first place.
3. Gas Supply Issues
The furnace needs a consistent gas supply to light up the flame and operate. If the consistent supply gets disrupted, the flame may fail to ignite or die out.
When the gas pressure gets low, there isn’t enough gas available to trigger the flame. In the case of closed gas valves, no gas can flow either. Additionally, the gas valve itself can malfunction and prevent gas from flowing when it should be open.
4. Airflow Problems
The combustion process also needs proper airflow. It is also necessary for ventilation.
A dirty air filter directly blocks the airflow. It can also lead to overheating and trigger a lockout. If the vents aren’t working properly, the combustion gases can’t escape and the furnace shuts down.
5. Other Safety Devices
Limit switches track the temperature inside the furnace and pressure switches monitor the pressure in vents. If these switches malfunction, because of blockage or other factors, the whole furnace operation shuts down.
The control board is the central device of the furnace. Any issue on the control board causes the furnace to malfunction; including ignition lockout.
Check out our infographic on 3 Main Causes Furnace Ignition Lockout
How to Fix Furnace Ignition Lockout
The reason behind the ignition lockout on a furnace can vary; some are minor for DIY attempts. A few simple steps can get your furnace running. Even with larger issues, these steps are worth a try to fix the furnace ignition lockout:
Note: Always turn off the furnace before working with it.
1. Reset the Furnace
Turn off the power and wait between one and three minutes before switching it back on. Then, turn up the heat in the thermostat to see if it starts correctly.
2. Clean the Flame Sensor
The flame sensor is in the burners. Turn off the furnace’s power and unscrew the flame sensors. Then, remove any soot or carbon deposits from the rod. Reinstall it and start the furnace again. To learn more, read our detailed step-by-step guideline on how to clean your gas furnace flame sensor.
3. Check the Igniter or Pilot Light
Modern furnaces have igniters and older versions have pilot lights. First, visually inspect them for damage. Then examine the igniter for continuity using a multimeter. Any fault in these two steps needs the replacement of the igniter.
Use the manufacturer’s instructions to safely relight the pilot. If it continues to go out, you need a replacement.
4. Ensure Proper Airflow
Check the air filter or vents for blockage regardless of the previous steps. The air filter is located on the retained air duct or side of the furnace. If you maintain your furnace properly, this should be the least of your concerns.
5. Check the Gas Supply
Make sure the gas valve is open for proper gas flow. If you smell gas, call a professional and after turning off the gas supply.
When to Call a Professional
If none of the troubleshooting methods work, your problem lies in the electrical connections or other issues. In that case, it’s best to contact a professional.
Here is the checklist to call for professional help in ignition lockout of a furnace:
- If you are not comfortable working with your furnace.
- If you smell gas.
- If you suspect major problems with parts like gas valves, heat exchangers, etc.
- If any DIY method is working temporarily, but the furnace keeps locking out after some time.
- If you have completed all the troubleshooting instructions and the furnace is still going into lockout.
Get regular professional tune-ups to avoid furnace ignition lockout in the first place. Professionals like Green Leaf Air can find any minor issues in regular maintenance to prevent them from causing a lockout in the future.
Conclusion
Furnace ignition lockout can be frustrating, but it plays a key role in keeping your home safe. Fixing it often comes down to simple steps like cleaning, checking components, or resetting the system. Regular maintenance prevents furnace issues and keeps it running smoothly. If a problem seems too complex, don’t hesitate to call a professional. A reliable furnace means a warm, safe, and worry-free home.
FAQs
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Is furnace ignition lockout dangerous?
A furnace ignition lockout can be dangerous if the root cause isn’t addressed. It is a safety feature to prevent any hazard. The event is protecting you from dangerous situations, so you need to take the issue seriously.
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Can I fix the furnace ignition lockout myself?
The cause behind the lockout can vary. For minor causes, you can perform some DIY fixes. Follow the troubleshooting steps in the fix section described in this article. If you are unsure about any of the steps or the furnace is still not responding, you should call a professional.
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How much does it cost to repair furnace lockout issues?
The cost of fixing furnace lockout issues vary widely. Usually, the costs involved are the part replacement cost and labor cost. For small replacements like air filters or flame sensors, you can save on labor costs and invest in just the part. However, always get professional help with any major part replacement.
