How Does a Furnace Gas Valve Work?

The gas valve on your furnace is one of the most important parts.

It is ultimately responsible for delivering an adjusting the flow of gas pressure to your furnace to keep it lit when running.

A gas valve replacement is a common furnace repair in older furnaces or when a gas leak is present.

Let’s take a look at the different kinds and how they work to keep your home warm in the winter!

Types of Gas Valves

Combination gas valve: This type of gas valve was introduced around the 1960s.

A combination gas valve contains a handle, a thermocouple, a regulator, and a solenoid valve.

In essence, it contains everything needed for the operation of a gas fired furnace.

Gas chain: These types of gas valves are quite common and require the operator to manually turn a valve to open or close the flow of gas to the furnace.

Once opened by the user, the solenoid valve will only open to allow gas to flow when the furnace actually calls for heat.

Otherwise, you’d have a non-stop flow of gas into your home!

A safety switch will only remain open if the thermocouple is heated to a minimum temperature, verifying the furnace is actually in heating mode.

How The Gas Valve Works

The furnace’s gas valve is operated by electromagnets.

There are two different valve’s that work in time with each other to provide the right amount of gas to your furnace.

The safety valve is what actually supplies the gas to the pilot light that will ignite the furnace burners during operation.

The other valve, the main valve, is what permits gas to be delivered to the burners themselves.

Your furnace has it’s own built in safety system via the thermocouple.

This little rod basically lets the gas valve know whether or not combustion (fire) is actually happening or not and whether the gas valve should remain open or closed.

If the thermocouple does not maintain a certain temperature, it knows that no combustion (fire) is happening and the gas valve closes to prevent gas from just leaking into your home for no reason.

How does a gas valve work?

In a nut shell: The gas valve’s thermal well senses the temperature of the water inside the water heater. If the temperature of the water is below the desired temperature setting indicated by the dial on the gas control valve, the gas valve will open the gas supply line, feeding gas into the burner chamber via the burner tube (aka burner manifold tube) so that the burner will be lit/remain lit by the pilot assembly’s ignitor. During this process, the pilot assembly and thermal well send electric signals to the gas valve to ensure that the unit is operating safely, and to tell the gas valve when to stop allowing gas into the burner assembly.

What should the light on a gas valve do?

If your gas valve has a status light, the light should normally be green or blue. Also, it should flash, typically once every four seconds, indicating that the water heater is idle; alternatively, the light may also alternate from bright to dim, indicating that the unit is heating water. If the light is off, there is no electrical power to the unit; if there is any other flash sequence or the light is red, there is likely an issue with your unit. For details regarding your specific unit, please refer to your installation manual, where you can typically find a diagnostic and troubleshooting chart; some gas valve models may also have a label with flash codes and explanations directly on their face plate.  

How do I know if my water heater’s gas valve needs to be replaced?

The most common indications that your gas valve needs to be replaced include:

-      Gas valve related flash code (see Flash Code Section below)

-      No hot water or inconsistent hot water (although this could be caused by many other issues)

-      If you have changed the pilot assembly and still do not have a consistent flame, it is probably the gas valve 

How much do replacement gas valves cost?/Are replacement gas valves expensive?

This depends on three major factors: the age of the unit, the size of the unit, and the availability of the gas valve.

The cost of a residential gas valve is typically anywhere from $110.00 to $250.00 (or more) each. Prior to contacting a service provider, be sure to check and see if your water heater is still covered under warranty; during your phone call to the manufacturer, they may be able to confirm the diagnosis of a faulty gas valve and send you a replacement part. If your unit is still under warranty, they typically send the part for free, with the option to add expedited delivery for a fee.

The average gas valve replacement requires a technician to be on site for 45 to 60 minutes. In the event that you are responsible for the labor costs, a simple way to save some money of your service call will be to drain your water heater prior to the technician’s arrival; this way, they will be able to verify the faulty gas valve diagnosis, remove the old gas valve, install the new gas valve, re-fill your unit, check for gas leaks, and ensure that your unit is functioning properly without having to wait for the water to drain.