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Lennox Furnace Not Getting Gas? Common Causes and Fixes

Does your Lennox furnace turn on but doesn’t fire up? Well, chances are it’s not getting any gas. If a gas-fueled furnace can’t draw gas, it can’t ignite, meaning it can’t produce the necessary heat to warm your home. 

Your Lennox furnace isn’t getting gas because of a faulty gas valve, a blocked gas line, or the gas supply is switched off. Easy fixes include replacing the gas valve, unclogging the gas line, and switching the gas supply back on.

This guide will help you diagnose and fix the most common reasons behind a Lennox furnace not getting any gas.

Faulty Gas Valve

A furnace gas valve controls the gas that flows from the supply line into the system. If the valve is defective, your Lennox furnace won’t get enough gas to work. 

A couple of things can make a gas valve stop working correctly. For instance, the valve itself may simply be damaged or worn out because of a leak in the basement. A problem in the safety unit or the ignitor could also be to blame. 

If your Lennox furnace isn’t getting gas, it’s sometimes difficult to identify what the exact problem is. Lenox systems come with many safety features that shut the furnace down if a component malfunctions and puts the home in danger. 

So, if there’s a component that’s causing your unit not to get any gas, the entire system will shut off as a safety measure and often won’t come on until you fix the problem. 

How To Fix

Unless you know that the gas valve is causing the issue, contact an expert to inspect your Lennox furnace. Use a multimeter to test if the gas valve is faulty.

It’s worth noting that a gas valve is irreparable. So if yours is defective, you must replace it. Here’s how:

  1. Turn off the furnace’s power and shut off the gas supply.
  2. Unbolt the service panel to locate the gas valve. Your gas valve will be positioned near the ignitor or pilot light
  3. Pull off the two wires attached to the valve terminals. Mark where these wires are clipped to the valve so it can be easy for you to hook them back later. 
  4. Grab your multimeter and measure the gas valve voltage in millivolts. If the reading isn’t  between 145–195 millivolts, the valve is faulty and must be replaced. 
  5. Unbox the new gas valve and remove the inlet and outlet plugs.
  6. Attach the new valve and align it the same way as the old one.
  7. Turn the valve switch to the ON position.
  8. Put the service panel back on and switch on the gas supply and furnace.

Replacing a furnace gas valve can be a daunting task if you haven’t done it before; hence it’s best to leave it to an HVAC professional. 

But if you still want to give it a shot, here’s a video to walk you through:

Blocked Gas Line

A gas line is simply a pipe that transports gas from the main supply to your furnace. While blockages in gas lines are rare, they can still happen and need to be addressed to keep the heating system working optimally. They’re usually a result of gas building up over time. The gradual accumulation eventually affects the effective passage of gas from the heating unit. 

If your gas valve works fine and your Lennox furnace still doesn’t get any gas, the gas lines are likely obstructed. With heavy buildup in the pipes, chances are very little gas is reaching your heater or not getting there at all. 

Insufficient gas flow can affect components like the ignitor or the pilot, causing your furnace not to turn on. 

The gas may be exiting the line before the blockage. If that’s the case, you’ll probably smell the gas. However, this depends on where the leak is. If it’s in the yard, there’s a good chance you won’t be able to smell it. 

How To Fix

If you know where the clogging is, you can simply go ahead and unblock the gas pipe yourself. If not, have an expert do the work for you. 

I don’t recommend cleaning gas lines yourself —  if you don’t do it right, any remaining obstacles risk clogging the gas valve. This can result in the valve not functioning efficiently.

But if you’re determined to do it yourself, here’s how.

  1. Turn off the gas supply. 
  2. If you’re dealing with smaller gas pipes, say 3/8 or ½ inch (9.5–12.7 mm) flexible stainless steel or copper tubing, push a plastic probe through the line to clear the clog. 
  3. If the line is ½ inch (12.7 mm) or larger, you can use something wider to clear the pipe. In this case, even a ¼ inch (6.35 mm) diameter auger is enough. 
  4. Once the line is unblocked, turn the gas supply back on and start the furnace to see if it ignites.

The Gas Supply Is Switched Off

Sometimes the reason why your Lennox furnace isn’t getting gas could be something as simple as a switched-off gas supply. 

Maybe a repair guy turned the valve off and forgot to turn it back on. If the gas supply is turned off, there won’t be any fuel going into your furnace.

How To Fix

To check if your Lennox surface is getting any gas, check if other gas appliances in the house are working. If the main supply is turned off, even your hot water tank won’t work, assuming it runs on gas too.

Here’s how to fix this problem:

  1. Locate the gas shutoff valve. The easiest way to do this is to find your gas meter, typically located in the front or on the side of your house. 
  2. You should see a gas line connected to the meter. The shutoff valve will be positioned a few inches off the ground along the pipe. The control switch will be turned perpendicular to the gas line if the gas supply is shut off.
  3. Using a crescent wrench, turn the switch to point upward, parallel to the line (the ON position). Your gas appliances should now work, including your furnace. Consult an HVAC technician if the furnace still isn’t getting any gas. 

Switching the gas supply back on and getting things up and running again can sometimes present dangers, especially if you have multiple appliances running on gas. If possible, have this handled by a professional. 

If you think you can do it yourself, this short video will help you make the process less hazardous:

Conclusion

If your Lennox furnace isn’t getting gas, check to see the gas valve is in good condition, gas ways aren’t blocked, and gas is released from the source. 

While the troubleshooting steps laid out here can help you fix fundamental furnace gas issues, I advise having all gas-related problems addressed by a professional.

Author

  • Steve Rajeckas

    Steve Rajeckas is an HVAC hobbyist with an avid interest in learning innovative ways to keep rooms, buildings, and everything else at the optimal temperature. When he's not working on new posts for Temperature Master, he can be found reading books or exploring the outdoors.

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