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Pilot Light Problems on Gas Furnaces

Gas furnaces are known for their smooth operation and exceptional durability. Yet that doesn’t mean that certain problems won’t crop up from time to time. A non-functioning pilot light — one that simply refuses to stay lit — remains one of the most common of all gas furnace complaints.

Unfortunately, this otherwise minor issue can lead to serious inconveniences if not repaired quickly. If you would like to improve your knowledge of pilot light mechanics, as well as some of the common problems experienced by this crucial component, read on. This article will boost your HVAC knowledge so you get smooth, consistent results from your furnace.

Pilot Light Mechanics

The pilot light enables the combustion that takes place in your furnace’s heat-generating core. This small flame remains burning at all times, meaning that your furnace can initiate combustion at the drop of a hat. Yet if the pilot light should go out, your furnace will not be able to burn gas at all.

The pilot light emerges from the tip of a thin tube known as the pilot orifice. This component attaches to your furnace’s gas valve between its primary and secondary gates. The pilot light operates using a simple feedback system. As long as the flame remains lit, it triggers a nearby thermocouple to send an electrical impulse telling the first gate to remain open.

Should the pilot light go out, however, the thermocouple will cool down, and the gate will close. This safety mechanism ensures that raw gas will not flow out through the pilot orifice — a potentially deadly scenario. In this regard, the thermocouple represents one of the most important safety features of a furnace.

Thermocouple Problems

As vital as they are to the overall functioning of a furnace, the delicate nature of thermocouples means they are often a contributing factor in pilot light problems. For one thing, a critical internal component may have burned out, bringing the thermocouple to the end of its functional lifespan.

The thermocouple may also have become mechanically damaged in some fashion. Such damage often affects the tube that connects the thermocouple to the pilot orifice. If pinched, crimped, nicked, or otherwise damaged, this tube will no longer be able to conduct the necessary impulse telling the valve gate to stay open.

Another common issue involves a thermocouple with incorrect positioning. This scenario often occurs as the result of fasteners working loose over time. Should the thermocouple’s physical orientation shift significantly enough, the pilot light may not heat it sufficiently to keep the gas valve gate open.

This issue tends to manifest as a pilot light that goes out within seconds of being lit. The thermocouple isn’t receiving the necessary amount of heat to generate the impulse to keep the valve gate open. Remediating this issue may be as simple as repositioning the thermocouple and tightening up its fasteners.

Lighting Errors

Things get a little trickier in that a poorly positioned thermocouple is not the only thing that can cause a pilot light to repeatedly go out. In some cases, the fault lies with human error. Relighting a pilot involves pressing a special override button while holding a lighter or match to the tip of the orifice tube.

The override button acts to open up the first gas valve temporarily. The trick to relighting a pilot light is to keep holding the override button after the flame appears for several seconds. This gives the thermocouple time to heat up and keep the gate open.


By understanding the components that make up a furnace, you can do a lot to prevent common problems. However, sometimes it’s just better to call a professional for help. For more help troubleshooting a problematic gas furnace, please don’t hesitate to contact the experts at JR Putman Plumbing, Heating and Air.

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