Lennox Furnace Code H35: What It Means and How to Fix It

The Lennox furnace code H35 error is one of several errors that can appear on your furnace’s control panel. This particular error isn’t a dangerous situation, but it does mean that you will need to troubleshoot the problem and take action as soon as possible. Lennox furnaces are some of the most reliable units you can buy, especially if you buy them from an authorized dealer or installer. However, even a top-of-the-line system can develop issues at any time. A red light appearing on your Lennox furnace means there is some type of problem with one of its sensors or other components. In this blog post, we’ll go over what the H35 code means on your furnace, how to troubleshoot it, and what to do if you continue to have problems after taking these actions.

What Does the H35 Code Mean?

Before we get into how to fix the Lennox furnace code H35, we should first understand what this error means. The Lennox H35 error indicates that the furnace has detected a problem with its gas-pressure sensor. This particular sensor is what helps the furnace regulate the amount of gas it uses to run and to maintain a safe and comfortable temperature in your home. The H35 error can also indicate that the sensor is shorted out. This means it could be letting too much gas through, which could be a fire hazard. If you have the H35 error, you must contact an HVAC professional to check the sensor and make sure it isn’t shorted out.

How to Fix the H35 Error

If you have the H35 error on your furnace control panel, the first thing you should do is check to make sure the sensor isn’t blocked or clogged. Sometimes a sensor can get clogged or blocked by debris or dust, which will cause the sensor to stop functioning correctly. If you’ve verified that the sensor isn’t blocked, you should also check the sensor wires to make sure they aren’t broken. If they are broken, you can replace the sensor, but if they aren’t, you should try to clean them to see if that will fix the problem. If you’ve verified that the sensor isn’t blocked and the wires are still intact, you may need to replace the sensor entirely. If you replace the sensor, be sure to clean the area around it to prevent the same issue from happening again.

How to Troubleshoot a Furnace with Code H35

You may be wondering how you go about troubleshooting the H35 error on your Lennox furnace. The first thing you should do is check the sensor wires to see if they are clean and if they are plugged into the sensor securely. If they are clean but are still unplugged, plug them back in. If they are dirty, try cleaning them with an electrical cleaner and make sure they are completely plugged in. If the wires to the sensor are fine, you should also check the sensor itself to make sure it isn’t broken. If the sensor is broken, you can replace it, but if it is clean and intact, you may need to replace the sensor.

Step 2: Check the Gas Vents

Next, you should check the gas vents to make sure they are not clogged or obstructed. If the vents are clogged, clear them out to keep the furnace from using too much gas. This will also help avoid the H35 error in the future. If the vents are clean, you may need to replace them to prevent the sensor from being blocked again. Replacing the gas vents will help reduce the risk of clogging and will help the sensor function as it should.

Step 3: Repeat Step 2 for Each Sensor

After you’ve checked the gas vents, you should repeat the same process for each of the other sensors to make sure they are clean and functional. If one sensor is broken, it might be causing the H35 error, but it also might be preventing other sensors from working properly as well. Make sure each sensor is clean and that each wire is plugged in properly to avoid triggering the H35 error.

Step 4: Reset the Computer

If you’ve checked all of the sensors and made sure they are clean and plugged in and you are still getting the H35 error, you should reset the computer. To reset the computer, shut off the furnace, unplug it, and then hold down the “reset” button for about 10 seconds. You can plug the furnace back in, turn it back on, and the error should be gone.


It’s important to remember that every furnace will break down eventually. This doesn’t mean that you should just accept it or try to ignore it. Instead, you should troubleshoot the problem as soon as you can. If you catch a problem early, it’s much easier to fix than if you wait too long. You should also be sure to get your furnace serviced by a professional on a regular basis. Preventing problems before they start will save you a ton of time, money, and hassle. If you have the H35 error on your Lennox furnace, don’t wait to troubleshoot the problem. The sooner you address it, the easier it will be to fix.