How the Pilot Light Works In Your Furnace

Modern furnaces use one of two ignition systems: Electronic for newer models and a pilot light for older furnaces.

In systems that use natural gas, the pilot light sets off the combustion process that helps heat your home. Yet due to age or lack of maintenance, it can experience a number of issues. Here’s what you should know about the pilot light.

What Is the Pilot Light?

Older furnaces with an annual fuel utilization efficiency (AFUE) rating under 80 percent include a pilot light. It’s a small, blue, constant flame inside the furnace that ignites the gas flowing into the burner.

When you turn on the furnace to heat your home, gas passes through a valve into the burner area. The gas meets the pilot light here, which ignites to generate heat. This process then warms the air circulating through your home.

Natural gas also powers the pilot light through a tube that passes from your home’s gas pipe. Working in conjunction with a valve, the thermocouple functions as a safety mechanism to monitor and halt the stream of gas if the pilot light burns out. Without this safety feature, gas would continue to accumulate in your furnace and eventually your home.

How the Pilot Light Operates

For the pilot light’s flame to be created, gas travels in a constant flow from a small tube. The gas is lit, allowing for a flame to exist at all times until it blows out. When this occurs, the valve traveling to the pilot light immediately cuts off the supply of gas.

The thermocouple provides the electricity that allows the valve to sense the delivery of gas, the presence of a flame and turn off once it goes out. In this instance, the thermocouple located near the flame cools down and stops generating electricity, which causes the valve to close.

Due to issues with gas being released, the pilot light needs to be relit. This involves opening the valve flowing to the pilot light manually, then lighting it. At this point, the thermocouple will heat up, causing the valve to stay open and power the pilot light.

Issues with the Pilot Light

Blowing out is the most common issue with pilot lights. While they can be relit, concerns surrounding operation emerge when the light continues to blow out or turn off. This can be attributed to the following scenarios:

• Airflow: The issue might be as simple as airflow repeatedly causing the pilot light to burn out. Specifically, your HVAC system may have leaky ducts, causing outside air to come through, or your chimney may be damaged.
• The gas was shut off: In more direct cases, the gas to your home or the furnace was shut off. If you cannot do this yourself, a professional can provide assistance. Beyond your control, this may be due to a shortage of natural gas in your area. At this point, you may need to reach out to your local utility company.
• The furnace has not been cleaned: Maintenance helps your furnace run more efficiently. When it comes to the pilot light, dirt can gather in the pipe traveling directly there. This reduces the amount of natural gas delivered, decreasing the size of the flame and how well the furnace generates heat. A red or yellow flame is a sign of insufficient fuel.
• Faulty thermocouple: If a pilot light will not stay lit, significant wear on the thermocouple may prevent the part from operating optimally, or it may have become loose.

If your pilot light experiences any of these issues, a small amount of carbon monoxide may be released into your home. Reach out to the HVAC professionals at MJ Fahy & Sons to inspect your furnace and recommend repairs, part replacement or a thorough cleaning. To schedule an appointment, contact us today.