As the weather gets colder, you turn your furnace on to keep yourself comfortably warm. Yet, at the same time, keeping your safety in mind is also important. One way to ensure the safety of your home is to ensure that your furnace flame sensor is working properly. This flame sensor is one of your furnace’s most important safety devices. Without it, you run the risk of dangerous gas leaks or explosions. Also, knowing why this component is necessary for furnace operation can help you identify when the flame sensor is faulty. Read this article to understand better this safety device and how to diagnose a problem quickly.

What Is a Furnace Flame Sensor?

Located within a furnace’s burner assembly is an important safety component called a flame sensor (or flame rod). This device monitors whether or not an active flame is burning within it. Should no flame be present, it will immediately shut off to prevent gas leaks and carbon monoxide poisoning of those inside. In such a way, this flame sensor helps protect against explosions that could potentially happen.

Thermocouple and Furnace Flame Sensor

When trying to repair or replace the safety component of your furnace, it is important to be aware of the difference between flame sensors and thermocouples. Although commonly referred to interchangeably, they are not the same components. Therefore, knowing which one you have is essential before attempting any maintenance.


The thermocouple is an essential safety feature on older models of gas furnaces. It operates by maintaining an always-burning small flame at its tip. That ensures that the top of the thermocouple stays warm and active for shutting off the furnace’s gas valve when needed. Should the tiny flame be extinguished, the thermocouple will become cooler and automatically shut down the system.

Furnace Flame Sensor

Modern furnaces are equipped with flame sensors. Instead of the conventional standing pilot light, these models operate via an electronic ignition that uses electronic igniters to light the gas. The purpose of the sensor is to check that the burners are igniting the gas correctly; and, if it detects a burner failure, to turn off the gas supply.

Symptoms of a Failing Furnace Safety Sensor

When it comes to HVAC components, the furnace flame sensor is no exception at all; it can malfunction. Flame sensors can fail without warning from age or extreme temperature changes. So, what should you look for if your furnace stops its normal operations? The signs of a broken flame sensor include:

Yellow flame

The burner flames should be blue — any yellow tinges mean the fuel is not completely burning away. That indicates that carbon monoxide is not properly leaving the system. For a long-term solution, contact a certified technician for a furnace flame sensor inspection or gas burner cleaning. While waiting for furnace servicing, keep an eye on your home’s carbon monoxide detector readings to ensure safety.

Increased energy bills

High heating bills during normal winter temperatures indicate something may be amiss in your furnace. The first step you should take is to make sure that the air filters are clean. Another reason could be an underlying problem with the flame sensor, which stops your system from working properly. We recommend getting a certified HVAC professional to check out this component and other parts of your heating system.

Rusty and corroded flue lines

Rusty and corroded flue lines can be another indication of inadequate furnace venting. The flue system is necessary for directing the potentially lethal CO gas out of your home. A leak in this system may be causing rust to form on your flue lines, meaning that the CO gas has nowhere to escape. Seek help from a professional to see whether you may require flue maintenance services.

Upgrade Your Old Heating System

Replace your aging gas furnace with a more energy-efficient model before it has a chance to fail unexpectedly. Doing so will help you avoid the headache and stress of an unexpected furnace breakdown. Contact a licensed HVAC contractor to replace your heating system. Since most furnaces have an estimated lifespan of 20 years or more, now could be the ideal time to make this change.

Furnace Repair Near Me

Is your furnace acting up? Or do you need help replacing your furnace flame sensor? Pioneers Heating and Air is a trusted name in furnace repair and installation in Pasadena and Altadena, CA. Our technicians are experts in furnace flame sensor replacement and repair to keep your home or business comfortable all winter. We also offer free estimates on new furnace options and heating repairs. Call us today at (626) 217-0559 for all your heating needs!

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