A furnace relies on a constant gas supply to function. As gas flows into the ignitor, a spark is created, allowing for flames on the burner. When there is no gas coming to the furnace, your home will not be heated, as no flames can be created. Fixing the issue is important – especially when it’s cold out.
If there is no gas coming to your furnace, you should check the gas valve, see if the limit switch is open, and get a reading on the voltage at the wires that supply the gas valve with power. If you’re not experienced in furnace repair, hiring an HVAC technician is the safest course of action.
In this article, I’ll walk you through the most common causes for this issue. I’ll also explain the most effective fixes for each of these problems. Let’s get started!
Faulty Gas Valve
The gas supply is attached to a special valve. This valve opens up in response to the control board. When the valve opens, it allows gas to pass through to the ignitor.
The gas valve usually works on its own. When you switch the furnace on, it will be opened automatically. In some cases, however, you may find that the valve is not opening up. This means gas cannot pass through to the furnace, resulting in no ignition.
There are a few possibilities to consider in this situation. Start by considering the valve itself. Many people find that when faced with this particular issue, the valve is faulty. This means the valve cannot open properly when the control board sends a signal.
How To Fix
Some people would advise you to give the gas valve a “whack.” When you do this, it is important not to end up damaging the furnace or gas supply. This could also be dangerous – for example, hitting the valve could cause it to break off, resulting in a rush of gas pushing through.
A gentle tap on the valve should be used instead. See if this fixes the problem. You do need to consider the possibility that the gas valve is faulty. In this situation, you may need to get the valve replaced.
- Start by switching off the furnace.
- Open up the furnace door and locate the gas valve.
- You will need to remove all wiring attached to the gas valve. The gas supply tube also needs to be removed.
- Remove the gas valve from the furnace and replace it with the new one.
- Reattach all appropriate wires, as well as the gas supply tube.
The process of replacing a faulty gas valve can be a bit complex.
Here’s a video to help guide you through a visual demonstration:
A Faulty Control Board
When the gas valve refuses to open up and allow gas to pass through, consider more than just a faulty valve.
While it is common for the valve to be faulty in this situation, note that the control board can be the issue.
When you turn the furnace on, a signal is sent from the control board to the gas valve. This signal allows the valve to open up and allow gas to flow into the system. If there is no signal sent to the gas valve, then it will not open.
It is possible to test for a faulty control board. This helps you ensure you do not initiate a replacement when you are not completely sure you found the issue at hand.
How To Fix
You will need a multimeter to test for a faulty control board. The process is relatively simple if you have one of these devices.
- The first step is to get to the gas valve. Open the furnace door and locate the valve. There is no need to remove the gas valve for this test.
- Use a multimeter to test the voltage at the two wires that run from the control board toward the valve.
- If you find that no voltage reading is provided or get a low voltage reading, then the control board is likely the problem.
The best solution in this scenario would be to get the control board replaced.
Limit Switch Is Open or Tripped
Most furnaces come with a built-in limit switch. This switch plays an important role in your home’s safety and the setup of your HVAC system.
When the furnace gets too warm, then the limit switch will be triggered. This is sometimes called an open limit switch. The limit switch helps to prevent the furnace from overheating. An overheating furnace may suffer damage or cause problems throughout your home.
If the limit switch is tripped, then the gas supply will be cut off.
How To Fix
The limit switch will either need to be reset or replaced in this case.
- Your first step should be to reset the switch and see if that solves your problem.
- Refer to your owner’s manual to gain access to the limit switch.
- Check if the limit switch is open. If it is, then follow the appropriate procedure to reset the limit switch.
- Turn the furnace back on and see if it is working now. If you see a flame, then it means the gas supply has been restored.
- The limit switch may be faulty too. If the furnace doesn’t ignite after resetting the limit switch, see if it tripped again.
- When the limit switch keeps tripping, there is a problem with overheating, or you need to replace the switch.
Here’s a video that guides you through the repairing and replacement process:
The Gas Reserve Is Empty
The gas tank used in the furnace can only hold a limited amount of gas. When this gas runs out, nothing is left to push the furnace when you switch the system.
It is always a good idea to check the gas tank’s level frequently. Some furnaces can warn you when the gas reserve is running low. This is a helpful way to determine when a refill is necessary.
How To Fix
Checking the gas reserves depend on the model you use in your home. Some furnaces provide an automatic overview of the gas levels. With other furnaces, the process can be a bit more complex.
- If the furnace has a notification system that signals gas, see if the light is on. The light will usually be red if the gas reserves are running low.
- If there is no such notification light, then consider checking the gas tank itself. Sometimes, you may find that there is a pressure meter attached to the tank. This meter may provide you with details on the current level of gas left inside.
- If the gas reserve is running low, get it refilled.
When there is no gas coming to the furnace, start by checking the gas valve. The valve may be faulty, or the control board may fail to signal the valve. The fault may also lie with the limit switch.
The replacement of a valve or control board requires technical knowledge. Turning to a professional is usually the best approach, as trying to fix this issue yourself may put your own safety on the line and even cause more damage to the system.