How Does A Furnace Gas Valve Work? A Complete Guide

Rima Chatterjee

Introduction to Furnace Gas Valve

Gas valves are key parts for a furnace. They control gas flow and make sure the furnace works properly. There are manual valves, combination gas valves, and solenoid valves.

To get the furnace going, the pilot light needs to light up first. Then, the burners ignite in order. Heat from burning is sent through the heat exchanger and circulated around your home with an inducer motor, blower fan, or gravity.

Safety measures are included in gas valve systems to stop potential dangers, like explosions or leaks. The pilot safety valve turns off the gas if there isn’t a pilot light. High limit switches switch off if temperatures are too high.

Some standalone gas valves can monitor system pressures and provide backflow protection for buildings, boilers, and water heaters.

Do you want a valve that does it all? Pilot light, pressure switch, solenoid valve, and safety valve all in one.

Image of a furnace gas valve

Components of a Furnace Gas Valve

To understand the components of a furnace gas valve with manual valve, combination gas valve, solenoid valve, pressure switch, inducer motor, ignition controller, pilot light and safety, flame sensor and thermocouple, we will break down how each of these parts work together to ensure proper heat distribution in your home.

Manual Valve

A furnace gas valve is a must-have for your heating system. It manages the flow of gas to the burner and creates a safe atmosphere for your family. The manual valve is responsible for controlling the on/off function. You can use it to start and stop the heating, which saves energy bills.

The manual valve stops dangerous gas leaks by completely cutting off gas supply. It’s designed with an ergonomic handle, so you can turn the valve easily without burning your hands. Plus, it needs no electricity or batteries, making it efficient and reliable.

Experts recommend you regularly check the manual valve for any signs of wear and tear. If you spot anything wrong, replace it quickly.

Choose your new manual valve wisely. Not all models fit all types of furnaces. Consider size, gas type (natural or LPG) and adjustable screw limits to control both high and low fire positions.

Combination Gas Valve

A Combination Gas Valve is a key piece of a furnace. It manages the gas flow going into the burner while keeping safety a priority. 

Check out the table below for the main elements of this valve:

Gas CockOn/off switch for gas supply
Pressure RegulatorKeeps constant gas pressure in the gas train
Solenoid ValveControls gas flow to the main burner
Safety Shutoff ValveStops gas when there’s a malfunction or risky situation

Be aware that some combination valves could have extra components, like a pilot shutoff valve or ignition control module.

Remember that these valves should be regularly inspected and taken care of by qualified people. This way, they will work correctly and avoid dangerous scenarios.

I remember when my neighbor attempted to repair their furnace but ended up damaging the combination gas valve. We had to call a technician and pay for costly repairs. It demonstrates how important it is to leave this type of job for professionals.

And, if the solenoid valve on your furnace gas valve starts making more noise than your mother-in-law, you are in serious trouble.

Solenoid Valve

The Solenoid Valve is an essential part of a furnace gas valve. It works by controlling the flow of gas to the furnace’s burners with an electro-magnetic reaction. 

Here are some important details:

Operating Voltage12VDC, 24VDC, 120VAC, 220-240VAC
Orifice Size0.4mm to 5mm (depending)
SealsNitrile, Neoprene, Viton, EPDM (depending)

Surprisingly, solenoid valves can also be found in washing machines and fridges. They can control the flow of water and refrigerant just like in a furnace. Did you know that they were first used in the mid-19th century

Back then, it was for telegraphy. But later, their use expanded into industrial areas like fluid and gas control. Nowadays, they remain an important component in several modern technologies, like furnace gas valves. The solenoid valve is under a lot of pressure. Let’s hope it can cope.

Pressure Switch

A pressure switch is needed to regulate the gas flow in your furnace. It automatically shuts off the gas when it detects low or high pressure. It’s important to know the type, material, function, and operating pressure of this switch.

The material determines the switch’s durability and reliability. A well-calibrated switch maintains safe operation and efficiency.

Issues like inadequate heat, continuous flame ignition, or excessive energy usage can mean your pressure switch isn’t working. Maintenance checks help avoid sudden failures and costly repairs.

Check for debris in the sensing lines so they’re clear of blockages. Also, stick to manufacturer replacement recommendations.

To keep your furnace healthy, understand how individual components work. Regular maintenance and replacements will help it run optimally throughout its life cycle.

Inducer Motor

The Inducer Motor is a vital part of a furnace gas valve. It pulls combustion gases from the heat exchanger and out through the exhaust. This creates a negative pressure that sucks in fresh air, allowing continuous burning.

This motor also offers safety. It stops backdraft and accumulation of toxic fumes in the heat exchanger and living space. Materials used for construction create consistent performance at low speeds and reduce vibration and noise.

The Inducer Motor saw its first major use in heating systems in the 1950s. Lennox Industries made high-efficiency residential furnaces and the induction draft fan. It decreased carbon monoxide, boosted efficiency and made quieter operation than before.

Ignition Controller

Ignition Controllers have critical specifications. Like a gas valve relay to regulate gas flow, a flame sensor to check if a flame is present, an ignition transformer to ignite the fuel-air mixture and a control board to ‘tell’ other furnace parts what to do.

It’s important to keep an Ignition Controller clean and in good condition, as dirt or wear can disrupt its ability to ignite the furnace. After installation, a professional should do a safety checkup to make sure all connections are secure.

For surefire safety, trust that tiny flame.

Pilot Light and Safety

In every furnace, the pilot light is an essential component for safety. It’s a small flame inside the gas furnace that ignites the burners when you turn up the thermostat. The pilot light also serves as a safety feature, if it goes out, a safety valve shuts off the gas supply to protect your home. It’s crucial to keep this flame lit and safe.

The thermocouple is another crucial safety device. It acts as a sensor, measuring changes in temperature from the pilot flame. If there’s not enough heat, it signals to shut off valves to prevent gas leaking into your home. Some furnaces have advanced features like pressure regulators and automatic shutoffs too.

Thanks to technology, furnace accidents are fewer than ever. The United States Consumer Product Safety Commission states that from 2009-2018, gas furnaces caused an average of 26 deaths per year. In Maine, only old-fashioned furnace designs are allowed; this ensures they can be used during power outages.

Flame Sensor and Thermocouple

Behold the flame sensor and thermocouple, two essential components of a furnace gas valve. The flame sensor detects the presence or absence of flames to prevent gas leakage. The thermocouple transforms temperature differences into electrical signals that keep the gas valve open.

But beware. Over time, corrosion or breakage can lead to unstable or nonexistent electrical signals. So, keep these components in top shape by regularly checking them and don’t hesitate to seek professional help when needed. It’s the best way to protect your home and your family.

How Does a Furnace Gas Valve Work?

To understand how a furnace gas valve works, let me explain the gas chain valve sequence, starting process, operating process, low fire operation, and high fire operation. 

These are the key things to know in order to comprehend the furnace gas valve’s role in regulating gas flow, managing fuel systems, and controlling heat exchangers. 

Whether you’re troubleshooting issues or just curious about the components of your furnace, knowing these processes can help you understand the right process and components for the job.

The Gas Chain Valve Sequence

The gas chain valve sequence is super important for furnaces. It controls the flow of natural gas and regulates how much fuel reaches the burner. 

Let’s look closer at how it works.

Here’s a table with the sequence:

1Thermostat calls for heat
2Gas valve receives signal
3Pilot light ignites
4Main burner ignites
5Thermostat senses temp increase, turns off gas valve

Some furnaces use electronic ignition instead of the pilot light, so the sequence is a bit different. There’s no need for step three.

Modern furnaces have extra safety features, like limit switches that monitor flame sensors. If there are any problems, the burners shut off. That way, your furnace operates safely and reliably.

To sum it up, starting a furnace is like trying to wake a teenager on Monday morning. It takes some patience and time.

The Starting Process

Furnace gas valves are a key part of a heating system. Starting the process requires several steps to enable the furnace to turn on. 

Firstly, the thermostat sends an electrical signal to the gas valve, which opens and lets gas into the burners. Then, electronic ignition lights the burners, producing heat. When the thermostat senses the set temperature has been reached, it signals the gas valve to close, making the flame disappear.

To start your furnace and keep it running well, follow these steps:

  1. Power: Ensure your furnace has a continuous electricity or fuel supply.
  2. Check: Inspect all heating elements (e.g. pilot light) before starting.
  3. Settings: Adjust settings according to the weather.
  4. Gas Valve Control: Turn ON the gas valve control, this cylinder-like object controls the amount of fuel that goes through the burner.

The Operating Process

A furnace gas valve is a key component of a furnace. It uses an electromagnetic coil to open and close the small piston inside the valve. When the thermostat needs heat, the valve receives an electric signal. This allows gas to flow to the burner.

The flame sensor checks for flames and keeps the valve open if it senses them. This gives your home heat. It’s simple but essential for proper heating. It works with other components like flame sensors, for safe operation.

Fun fact: Faulty gas valves can cause heating system malfunctions, regular maintenance can help them last longer. Even furnaces have mood swings, Low Fire Operation is like a deep breath before a flame.

The Low Fire Operation

Gas valves are vital for controlling the flow of gas in furnaces. Low fire operation is vital for energy efficiency and optimal performance. It opens partially to let a small amount of fuel flow in. This setting maintains the minimum heat needed for comfort.

The opening of the gas valve changes the flame’s strength and intensity. So, only experienced technicians should adjust it. Gas valves are prone to wear and tear. Expert servicing of furnaces every two years helps reduce damage.

Homeowners must take regular precautions with HVAC systems. Lack of upkeep can lead to fatal events. Get ready. In the high fire operation, this gas valve is serious.

The High Fire Operation

The High Fire Operation has components with special functions. The gas valve controls the flow of gas to burners. The pressure switch regulates the pressure in the system. The draft inducer motor draws air into the flue. The igniter starts the combustion.

When The High Fire Operation begins, gas flows into the combustion chamber. The pressure switch makes sure there’s enough pressure for perfect combustion. The draft inducer motor gets rid of any left over gases. When there is enough gas, the igniter sparks and creates heat.

It is important to keep the furnace’s gas valve in good condition. You should get it checked by a professional. Also, clean your filters as dirt can reduce airflow leading to incomplete combustion.

If your furnace gas valve is acting weird, it could be trying to gaslight you.

Common Issues with Furnace Gas Valves

To troubleshoot common issues with furnace gas valves, you need to know how a furnace gas valve works. In order to solve the following issues, you must understand their root cause. 

Let’s dive into each of these sub-sections and figure out the right solution for your situation.

Gas Flow Issues

Gas flow issues in furnace gas valves can seriously affect a home’s heating efficiency. These can be inadequate gas flow, wrong pressure, or even full blockages. Regular maintenance and inspection are essential to prevent this. If your furnace doesn’t seem right, seek help quickly.

Clogging is a common problem with furnace gas valves. Reasons include dirt, rust, or general wear and tear. When this occurs, the valve may not work correctly, leading to gas flow problems. Moderate clogging may be possible to clean yourself. Severe damage should be handled by a technician.

Broken or blocked valves can cause gas leaks, which are dangerous. If you think there is an issue with your furnace’s gas valve, call a professional immediately.

My neighbor had furnace issues recently. He tried fixing it himself, but no luck. With winter coming, he called in a repairman who fixed his furnace in hours. The issue was a short circuit in the control board, preventing the spark for the furnace burner tubes. Experienced help is necessary for modern furnaces with sophisticated technology. Nothing like a gas leak to appreciate a functioning valve.

Appliance Leaks

Gas valves on furnaces can be a risky and pricey issue for homeowners. They let gas enter an appliance, but if they fail or break, it can lead to a gas leak and hazardous situations.

Keep an eye open for any issues with your furnace’s gas valve. If you smell something bad or hear a hissing noise, it could mean a gas leak. Get help from a professional technician right away.

Routine care of your furnace can help avoid problems with the gas valve. Still, troubles can arise even with maintenance. Have your system checked by an experienced technician who knows about furnaces and their parts.

In one case, faulty furnaces with gas leakage caused several deaths in a US rural area. Maintaining them correctly could have avoided such tragedy.

Backflow Problems

Furnace gas valves can have backflow problems. This is when the gas moves back into the fuel line, instead of out through the valve and into the furnace. This causes pilot lights to go out and a dangerous buildup of gas in your home.

A backflow preventer can help. It ensures that gas only goes in one direction. But, make sure it’s the right size and type for your furnace and fuel source.

Check for clogs or debris buildup in the valve. Routine maintenance prevents bigger issues later.

A customer experienced a gas smell in their home. It turned out to be a faulty gas valve that caused backflow. The consequences could have been severe, if not addressed quickly. Be aware of any strange smells or behaviors of your furnace and call for help if you suspect a problem.

Pressure Regulator Malfunctions

Furnace gas valves come with a pressure regulator. If it malfunctions, big problems can happen. A leak in the diaphragm may lead to uneven heating or even shutdown. The spring inside the regulator may also wear over time, causing the furnace to heat less.

To avoid these issues, regular maintenance is key. Check for leaks in the diaphragm and worn springs in the regulator. Have a professional make any adjustments to the regulator. This will ensure safe and effective furnace operation. Of course, if your heat exchanger goes out, you’ll save money in the form of funeral expense.

Heat Exchanger Issues

Heat exchanger issues are a common problem with furnace gas valves. 

We have put together a table to give an overview of the different issues.

IssueDescriptionPossible solution
CracksWear and tear can cause small or big cracks, which can lead to carbon monoxide leaks.Replace or repair by an HVAC professional.
CloggingDust and debris buildup reduces efficiency and causes uneven heating.Clean the heat exchanger by a technician, change filters regularly and maintain properly.
CorrosionMoisture, air quality or condensation can cause rusting or oxidation leading to holes.Preferably replace it as patches just fix it temporarily.

It’s wise to do regular maintenance checks to avoid any future complications.

The National Home Warranty Association conducted a study that said 49% of all home repairs are connected to HVAC systems.

How to Check and Replace a Furnace Gas Valve

To check and replace a furnace gas valve with precision, you need to know how it operates. Here’s how to do it systematically. 

In this section, I will explain the two sub-sections, checking the gas valve with a multimeter and replacing the furnace gas valve. Whether you’re dealing with a faulty furnace or just want to learn how to troubleshoot potential issues, this guide will help you get the job done right.

Checking the Gas Valve with a Multimeter

Checking the gas valve with a multimeter is key to keeping your furnace’s performance up. 

Here’s how to do it:

  1. Cut power: Make sure to turn off the power supply before any electrical work.
  2. Find the valve: Check the owner’s manual to locate the gas valve.
  3. Set the meter: Use your multimeter to measure DCV (Direct Current Voltage).
  4. Take a reading: Connect one lead to each terminal of the gas valve and take the reading.
  5. Check the VDC: If your reading is less than 3 VDC, then it’s time to replace the gas valve.

Safety first. When checking the gas valve, wear safety glasses and gloves. Avoid sparks by not touching wires or metal parts.

Pro Tip: If you’re not confident with these tasks, hire a licensed technician with furnace experience. A professional will have the knowledge and tools needed to repair your furnace safely and correctly.

Replacing the Furnace Gas Valve

Replacing a furnace gas valve is a must for homeowners. If the furnace stops working, then its valve may need to be replaced. 

Let’s explore how to detect and replace a faulty gas valve in furnaces.

  • Step 1: Shut off the furnace’s power. Do this to prevent any electrical injuries or accidents.
  • Step 2: Remove the old valve. Disconnect its wiring and unscrew it from the pipe.
  • Step 3: Set up the new valve. Install it onto the furnace in place of the old one. Make sure all connections are tightly secured to avoid gas leaks.
  • Step 4: Reconnect wiring. Do this before turning the furnace’s power back on.
  • Step 5: Test the furnace. Turn it on and make sure it works correctly. If there are still issues, call a professional technician to inspect.

Don’t forget to clean up any debris. Regularly check for propane leaks before testing. If you smell propane, immediately seek professional services instead of attempting repairs alone.

My friend once tried replacing his faulty valve without enough knowledge. He ended up risking his family’s safety. He eventually had to call someone over proving that some jobs are better left to professionals.

Remember, always prioritize safety when dealing with furnace gas valves. Otherwise, you’ll end up like a crispy critter.


Gas valves are key components of furnaces. They regulate fuel to the burners as per the thermostat’s temp settings. They can be manual or auto and used with other devices like pilot lights, controllers, and regulators. Read and follow manufacturer instructions for setup, operation, and care of your furnace valve. Check valves often for malfunction and leaks. These could cause fires or toxic gas backflow into living spaces. If you notice something strange like difficulty starting or smells, address it right away. Don’t do DIY repairs if you don’t know about gas systems. Some valves have two settings for different heat intensities. Low-fire mode uses less energy in mild weather and high-fire mode gives more heat in cold days. I once had a problem with a bad valve that stopped my furnace burner. It was a freezing night with no heating until the tech showed up. This made me realize the importance of maintenance and quick repairs to avoid such issues. Always put safety first when dealing with fuel appliances.

About the author

Debarghya Roy: A heating systems author, Passionate about energy efficiency and sustainability, Sharing insights and empowering readers through informative blog articles.