What to Do If the Furnace Gas Valve Does Not Open

We cover the possible reasons why it may happen and whether or not it is safe to fix it by yourself.
Carolina Evans
Carolina Evans
Research Writer
Holds a Master’s degree in Engineering and is keen on her own home’s climate. Sometimes we think that Carolina owns every single product she writes about – that’s ho read more
Reviewed By
Richard Powell
Richard Powell
Expert Consultant
For 8 years, Richard had been working as an HVAC specialist and AC unit installer since his student years. Now, he’s our main consultant on every technical aspect that may read more
Last updated: September 10, 2023
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One of the most reliable ways to heat your home and stay warm, especially during the winter months, is with a gas furnace or a heat pump. But even if they are known to be dependable systems, this doesn’t mean that they would always work. One of the most common problems is when the furnace gas valve is not opening, and it can be very frustrating. This is one of the occasional breakdowns that the gas furnace can have.

When you have the furnace gas valve not opening problem, you can end up spending a lot of money on trying to fix the valve so that the gas valve can work again. Even if you know what the problem is, you would still spend money hiring someone to fix it. Or, you can pick up some tools and solve the problem of why your gas valve is not opening. Let’s take a closer look at your options.

How Furnace Gas Valve Works

What to Do If the Furnace Gas Valve Does Not Open
Before figuring out what is wrong with your gas valve, you need to understand how the entire system works. The valve is an important part of the fuel system of your furnace. When it opens and closes, it makes room for the flow of gas to the burner and the pilot light. The gas valve works simply but is integral to your furnace. 

The furnace gas valve is made up of two valves, and they are positioned in series. It works with electromagnets. The first valve is the primary valve, which is the safety valve. It supplies gas to the pilot light. The second valve is the main valve, which lets gas flow to the burner tray.

The furnace gas valve also includes a thermocouple, which would create the power that keeps the safety valve open. If the thermocouple is not providing enough heat, the furnace gas valve would close, leading to a gas supply cut to the pilot light. With the thermocouple working perfectly, you can prevent gas from building up in the home.

Then for the main valve, you have the thermopile. The valve uses a larger tube than the pilot light valve that the thermocouple uses, to let gas through. The two valves are also part of the safety features of a furnace because if there is a problem, the main valve is closed while the pilot light valve is left open for safety.

So, the two furnace gas valves have their function in the furnace that makes the entire system work. If one valve isn’t working, then you can check if the pilot light valves or the main valves are not working any longer. 

If any of the valves are not working properly, it can release gas into your home and cause a dangerous accident. But most of the time, it simply prevents the furnace from working and leaves you in the cold weather.

There are different types of furnace gas valves that you might have to deal with when trying to fix the system. The gas chain of your furnace includes a manual valve, pilot safety, solenoid valve, and a combination gas valve. If your furnace has a gas chain valve system, you need to turn the valve open and close it manually. 

The design of a furnace would regulate the gas pressure and keep you safe and warm. Now that you know how the furnace gas valve works, we can move on to figuring what problems it has whenever it refuses to open. 

Possible Reasons Why a Gas Valve May Not Open

There are different reasons why your gas valve might not be opening, and it’s important to know what the causes are so that you can fix it or call an HVAC operator. Here are the possible reasons why it might not open.

  • Inadequate Heating to the Thermocouple

If your thermocouple is not generating enough voltage, the furnace gas valve would close and refuse to open. The thermocouple is meant to keep the safety valve open, and when there isn’t enough power for this to work, your valve won’t open. 

You would have to check if there’s enough power for your thermocouple to function effectively if your gas valve isn’t working. Simply check the manufacturer’s requirements for power and ensure your furnace is receiving the right amount of power. You should also check if other safety mechanisms in the circuit are getting the right voltage.

  • Faulty Thermostat

Another reason why your furnace gas valve is because the thermostat isn’t working ideally. When the thermostat signals to the furnace gas valve, it would open and close, ensuring that it lets out the right temperature into your home. So, if the thermostat isn’t working, then the furnace gas valves won’t open and you won’t get any heat.

If you realize that the thermostat isn’t working and decided to purchase a new one, keep in mind that it should be compatible with your furnace, so check the manufacturer’s requirements. Then, follow the manufacturer’s instructions and replace the thermostat so that it works properly again.

  • Open High Limit Switch
    What to Do If the Furnace Gas Valve Does Not Open

One of the safety features of a furnace gas valve system is the high limit switch, which would shut down the furnace if it gets too hot, like having a clogged air filter. If your high limit switch remains open even after your furnace is safe to use, the gas valves won’t open and you won’t be able to use the furnace.

The system would shut off power to the main furnace gas valve, so you can open up the switch. Check the manual of your furnace or ask your manufacturer how you can close the high limit switch so that the valves can open.

  • Faulty Draft Motor

The furnace gas valve also includes a draft motor or a draft inducer. The motor is used to pull in air and blow the air it collected out through the chimney or the vent. So, the vent would not be blocked, preventing the furnace from backing up and leading to a buildup of carbon monoxide. When the motor clears draft, it signals to the furnace gas valves which would then start releasing heat. 

When there is a problem with the draft motor, it won’t be able to indicate if the furnace should start or not. You can check if the draft motor is not coming on or if the vent is blocked which is why the valves are not getting a positive signal to start the furnace. So, it’s either you clean the furnace or you replace the motor.

How to Check if the Gas Valve Is Not Working

You can follow this sequence if you want to check whether the gas valve of your furnace is not working or not. It also checks if you need to get a replacement valve. Even if you find the problem with one of the earlier steps, it’s advisable to continue in case there are further issues with the gas valve.

  • Check the Wires

First things first are to check the wires of your furnace gas valve, as they might be frayed or cracked, stopping the valves from working. It might be because your furnace is old or too much electrical power burnt the wires. Replace the wires and carry on.

  • Check the Coil

The furnace gas valve features a coil, and this is the second thing you should check. If you have two-meter leads, you can check whether the coil’s resistance is bad or good by placing them on each terminal and checking the readings. 

  • Check the Utility Line Standard

Then, you can also check if the gas coming into the valve meets the utility line standards. You can look at the inlet side and check the port to check it. If it meets the utility line standards, you can move on to the next step.

  • Check the Burner Orifices 

Most furnaces also come with plugged burner orifices and if you’ve been using your furnace for a long time, insects, especially spiders, might have spun webs into the orifices. This would lead to gas valves not opening. Try to fire up the system by checking the burner orifices.

  • Check the Voltage 

If there is a drop in the voltage or gas pressure to the gas valves, they won’t open. This would make the furnace turn the flame on for a few seconds and turn off repeatedly. Look at the inlet and outlet side to see whether the pressure is dropping.

  • Check the Flame Sensor

Another reason why the gas valve could be opening a little to give you flame for a few seconds only to close and turn off again is that the flame sensor is faulty. You can check whether the sensor is faulty because if it is, it would signal the gas valves to shut down.

  • Check the Rollout Switch
    What to Do If the Furnace Gas Valve Does Not Open

If the flame in your furnace is only hitting the metal heat exchanger, the safety would trip, like the rollout switch. So, the gas valve would open a little and close repeatedly. You don’t have to remove the switch completely, only fix the problem. 

  • Check the High Limit Switch

As explored earlier, the high limit switch is another cause of the furnace gas valve, not opening. This safety trip can cause the gas valves to shut off, so check if it is open and do what you can do to close it according to the manufacturer’s instructions.

  • Check the Blower Motor Speed

Another thing you should check is the blower motor speed of your furnace as if it is too low, then the furnace gas valve won’t open. You can check your manual to see where the blower motor speed is.

  • Check the Ductwork

If the ductwork of your furnace is faulty, it can also cause the gas valve to close. Check if the ductwork feels questionable, and if it does, then you would have to fix it.

If you check all the problems with your furnace gas valve and it still isn’t opening, then you might have to condemn the entire system and replace your system completely with a new gas valve. This way, your furnace can work ideally with a new valve. You can also skip the entire process if you can’t want, and replace the gas valve, although this would be needlessly expensive, especially when it might just be a small problem. 

Can You Fix It by Yourself?

What to Do If the Furnace Gas Valve Does Not Open
If your furnace gas valve isn’t working and you know what the problem is, the next thing you do is either fix the problem yourself or call for an HVAC technician. You should only attempt to fix your furnace yourself if you have any technical knowledge. Without technical knowledge, you might be able to do certain things like clean out air filters or close the safety trips so that the valves can open again. You might also be able to increase the power of your thermocouple. 

Keep in mind that you shouldn’t do risky things like bang the gas valve with a wrench or use any other dangerous instruments to fix it. The furnace gas valve system is sensitive.

But with technical knowledge, you might be able to fix more complicated issues like the draft motor, thermostat, replacing wires, and other important parts of your furnace. This is only if you know what you’re doing with a furnace heating system.

We strongly advise you to call a professional HVAC technician. These technicians have what you need to pinpoint any problems with your gas valves and fix them in minutes. This is the safest way to fix or replace your furnace gas valve.

If you do so, you should check the price quote that they give you before you give the go-ahead for them to fix it. 

So, consider whether or not you can fix the problem yourself, and if you can, then you can take care of it. If not, you should settle for calling a professional to fix the problem.

Final Thoughts

Now that you know what to do to troubleshoot your furnace gas valve, you can stay warm whenever the winter months come up. Without your furnace or heat pump working perfectly, it would be difficult for you to take care of your family during the cold months. So, you should either check what the problem is or call for an HVAC technician instead. 

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