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Furnace Pilot Light: How to Re-Light, Fix and Protect Your System

If your furnace has a pilot light, chances are you’re going to need to re-light it at some point. In this article, we discuss why that happens and offer safety and maintenance tips.

Furnace Pilot Light: How to Re-Light, Fix and Protect Your System

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Roger Bakies


August 2nd, 2021

We only tend to think about pilot lights when they become a problem. The web is littered with searches for “how do you relight a pilot light?” and “why does my pilot light always go out?”

Our job as HVAC professionals is to demystify the equipment in your home and to educate you on subjects that people are asking about. That means tackling this issue head-on.

So that brings us to the pilot light. Let’s turn you into an expert on pilot lights, so you don’t have to feel anxiety the next time your system gives you trouble.

In this article, we’ll cover common questions related to pilot lights, including:

  • What they are
  • What function(s) they perform in your HVAC system
  • What systems are in place to ensure your safety
  • Why they go out
  • What to do when it goes out
  • Lastly, what steps to take to ensure that your pilot light doesn’t give you trouble anymore.

A woman sitting on a couch with a fur hood on her head

What Is a Pilot Light?

A pilot light is a type of igniter that’s typically found in older furnaces. Some of these furnaces could be as old as 30 years. It is simply a gas flame, which first means that it will only be present in gas HVAC systems. If your home runs solely on electric power, you won’t have a pilot light.

The light is an ignition source for the larger gas burners that are located inside your furnace. When your thermostat communicates to your furnace to turn on, these burners will light to provide heat from your home. But the larger burners can’t light unless the initial flame source—your pilot light—is working properly.

The most noticeable sign that your pilot light is out is when you feel air coming out of your vents, but it’s not warm. If it’s simply room-temperature air, your pilot light may be the cause of it.

Pilot lights are a dying breed in HVAC installation. Each year we see fewer and fewer furnaces with standing pilot lights. In Central Ohio, I’d say that only around 5% of the furnaces we see have pilot lights. Having a flame perpetually lit can be costly in the long run, burning up natural gas and increasing your utility bills slightly. In most modern equipment, an electric igniter is used, even in a furnace that uses natural gas.

Differentiating Usages of the Term Pilot Light

Occasionally “pilot light” can refer to the ignition source for other appliances, such as ovens or fireplaces. It can also be used to talk about an indicator light on a device, one that signals that the device has power and is functioning properly.

For our purposes, we’re only talking about the pilot light for your furnace.

How Are Pilot Lights Protected?

In any system with a pilot light, there will be at least one safety device present. This device is intended to detect the flame and acts as a cut-off switch if something is wrong.

The fear here is that if your pilot light isn’t lit, but the system is trying to heat, you may be releasing gas into your home. This presents a very clear danger, which is why it’s important to deal with a faulty pilot light immediately.

We’re going to discuss two similar safety devices below: flame sensors and thermocouples. We’ll talk about how each one works, and what measures are needed to fix them.

HVAC technician repairing a furnace

Thermocouples & Flame Sensors: What They Are and When They Go Bad

These two terms are often used interchangeably, but they’re slightly different. However, both refer to the safety devices that detect a working flame in your system.

Flame sensors are used on systems with an electric igniter. It detects whether or not the burners on your furnace are working properly. However, this is for the burners themselves, not a pilot light.

Thermocouples are sometimes called flame sensors, so don’t get confused if you hear the term but have a pilot light in your home. Thermocouples are copper rods that directly interface with the flame from the pilot light. If the light doesn’t hit the thermocouple, it will engage the safety trigger.

The difference in terms isn’t as important as knowing what type of furnace system you have so that you can properly assess the problem if you experience a lack of heat.

Why Does My Pilot Light Go Out?

There are several possible causes of a pilot light going out. While the list below isn’t necessarily exhaustive, it covers the most common causes associated with an extinguished pilot light:

  1. Dirty pilot light. The shaft that the light comes out of might contain debris of some sort. This can interfere with the light’s operation. You can often spot this even when the light is on. If there is noticeable flickering, one side seems to struggle to light, or the base of the flame is yellow instead of the hotter blue, you are likely dealing with some sort of blockage or buildup.
  2. Thermocouple Malfunction. Parts deteriorate over time. There’s no avoiding it. However, a failure in the thermocouple doesn’t necessarily mean it’s faulty. It may mean it’s simply off-center or needs to be cleaned thoroughly.
  3. Drafts. Don’t think it’s drafty in your basement or utility closet? Think again; it could be. We tend to think of drafts as coming from outside the home, but leaks in your ductwork or improper sizing in your return air supply can create an airflow that can extinguish a pilot light. If the materials like the light itself and thermocouple seem to be ok, you could have air leak issues that need to be inspected.
  4. Gas supply. This is rare but can affect any appliance that uses gas in your home. If your pilot light isn’t the only device you have issues with, it may be time to call your gas company to come out and inspect the line running to your home.

A close up of working burners in a furnace

Lighting a Pilot Light When It Goes Out

The good news here is, if it’s not a larger problem with a part or system, there are DIY solutions to relight a pilot light.

The bad news is that if it’s a larger problem like a busted part or leak, the only viable solution may be to call a professional to handle it.

Assuming yours is the easily fixable kind, here are some steps you can take to get it running properly again:

  1. Consult the Manual. If you still have your furnace’s manual, it should contain instructions for relighting the pilot light. This will be a better guide than anything you can find online because it will be specific to your system instead of general advice.
  2. Turn the Gas Off. And leave it off for at least five minutes. This is to allow any ambient gas to dissipate. Otherwise, you could harm yourself while relighting.
  3. Reset and Light. After five minutes, turn the gas back on to allow it to release from the pilot light orifice. Most systems have a dial that can be set to “Pilot” to allow for gas to flow again. There should also be a reset button that you’ll want to press. Once the system is reset, you can hold the flame of a long lighter (the kind typically used for grills) up to the pilot light, and it should come on.

There are similar processes for pilot lights on appliances like water heaters and ovens, but we’d encourage you to find resources on those appliances to make sure you’re accounting for any differences in the relighting process.

What If My Pilot Light Keeps Going Out?

If your pilot light refuses to stay lit, you may need to check the integrity of your furnace and ventilation system.

A few common reasons a pilot light may repeatedly go out include:

  • Changes in your ventilation system. Wind and precipitation can shift your ventilation covers, which further exposes your pilot light to the elements.
  • Issues with your thermocouple. A thermocouple is a safety device that senses when your pilot light is on. If your thermocouple is dirty, it may not be able to sense that the pilot is on. As a result, the gas valve turns off. If your system keeps trying to start before turning off again, there could be an issue with your thermocouple.
  • Issues with your gas valve. Your gas valve supplies fuel for your system. If neither your pilot light nor your system will turn start, there could be an issue with your gas valve.
  • Cracks in your heat exchanger. After years of heating up and cooling down, your heat exchanger may crack. These cracks can alter airflow within the system, which can extinguish your pilot light.

You’ll likely be able to check for small changes in your ventilation system, such as a missing rain cap, yourself. But a trained HVAC professional should diagnose more complex issues.

How Much Will It Cost to Fix a Pilot Light?

You should be able to replace a Type B vent cap for less than $50 depending on the size of the pipe. But replacing a masonry chimney cap, gas valve or heat exchanger can get a bit pricey.

Here’s how much it would cost to fix these issues:

  • Replacement chimney caps can cost between $35 - $750, depending on the material the cap is made of.
  • Replacement thermocouples can cost between $100 - $250.
  • Replacement gas valves start around $350.
  • Heat exchanger repairs start around $100 but can cost thousands of dollars. Repairing a heat exchanger is the HVAC equivalent of heart surgery: these are labor intensive repairs that require a highly skilled technician.
  • Replacement heat exchangers can cost $1,000 - $2,000 under warranty. But if your furnace’s parts aren’t under warranty, you could pay as much as $3,500 to replace your heat exchanger.

Depending on the brand, a heat exchanger may be covered under warranty for 20 years to the life of your system. It’s also important to remember that parts warranties typically don’t cover labor costs and other fees -- only the cost of the parts.

To check if your system is covered under warranty, you’ll need three things: the brand or manufacturer, your furnace’s model number, and your furnace’s serial number.

You should be able to obtain all of this information from your furnace’s data plate. In older furnaces, data plates are typically located inside the furnace’s cabinet.

To locate your furnace’s data plate, open its front panel. Often, you’ll be able to see the data plate on the left or right inner panels.

Safety & Maintenance Tips

As furnaces age, they may not work as well as they used to. If you have a furnace with a pilot light, your furnace has likely lived a good, long life. But if you’re not ready to replace just yet, let’s talk through safety and maintenance tips for furnaces with pilot lights.

1. Place carbon monoxide detectors near sleeping areas.

A pilot light can generate more carbon monoxide as the system ages. Because carbon monoxide is odorless, carbon monoxide detectors can alert you before you’re in danger of carbon monoxide poisoning.

But make sure that you place carbon monoxide detectors near the areas where you and your family sleep. This way, you’ll be more likely to hear the detectors no matter the time of day.

The CDC recommends using battery-powered carbon monoxide detectors. If you check the batteries when you change your clocks in the spring and fall, you can ensure that your detector is in working order.

If your carbon monoxide detector goes off, leave your home immediately and call 911.

2. Schedule regular maintenance for your system.

Regular maintenance can help systems run smoothly and efficiently for as long as possible.

Although regular tune-ups won’t make your system live forever, they can make a huge difference. Maintenance can identify issues before your system breaks down.

Regular maintenance can also catch high levels of carbon monoxide before they become deadly. During a routine tune-up, an HVAC technician should check your system’s performance. This includes checking how much carbon monoxide your system produces.

Regular maintenance also ensures that your furnace operates efficiently.

Furnaces with pilot lights could operate up to 50-70% efficiently in their prime. Although this is significantly less efficient than modern furnaces, you can conserve as much of that efficiency as possible with maintenance.

Your HVAC partner should clean your system during a furnace tune-up, which can play a large role in ensuring your system is operating properly. As your heat exchanger collects dirt, your system has to work harder to produce heat. This increases wear and tear on your system.

Because of the complexity of your system, you should avoid DIY maintenance unless you’re changing a filter.

Buy Your Filter

You should schedule maintenance for your home twice a year: once before the cooling season and once before the heating season.

This ensures that both your heating and cooling systems can operate properly when you need them

DIY vs. Professional HVAC Maintenance and Repair

There are some caveats to the process above that we’d be remiss in not mentioning:

  1. If the above process doesn’t work, consult a professional.
  2. If you are confused at all or worried about harming yourself or your home, consult a professional.
  3. Don’t use a traditional cigarette lighter, which can put your hand too close to the pilot light for safety.

HVAC equipment is very specialized and complicated. While safe, effective DIY solutions exist to relight your pilot light, the further you get into working with your equipment, the more likely you are to miss a crucial step.

Replacing a Pilot Light by Replacing Your Furnace

Did you know that an estimated half of a gas furnace’s energy consumption is from a pilot light that is perpetually lit?

Even if that estimate is high, there’s a reason pilot lights are seen less and less these days. The reason is that there are more efficient forms of technology available for your furnace. HVAC technology and equipment have come a long way even just in the last 10-20 years. And the difference results in better comfort and lower utilities for many families and homes.

What will your exact cost savings be? That’s hard to say precisely, because not all of your utility costs are from HVAC. Though it’s certainly possible to form a reasonable estimate based on your current system and energy usage.

RELATED: Will A New Furnace Save Me Money?

Of course, a new furnace is a significant investment, but if you’re expecting to stay in your home for several years or are fed up with your current equipment, now may be the best time to make the switch to something that will save you money and stress long-term.

RELATED: How Much Does a New Furnace Replacement Cost?

Maintaining Your HVAC System

Your pilot light is one of those things where, if it does go out, you may be able to handle it yourself. The truth, though, is that even for the DIYers out there, there are plenty of HVAC maintenance tasks you shouldn’t be handling on your own.

Far better than dealing with a faulty pilot light is making sure it’s not an issue in the first place. So our challenge to you is this: if your pilot light is out, make this the last time it ever happens.

How do you do that? By scheduling routine maintenance from a professional who’s going to know what to look for that could spell trouble. Cleaning, aligning and otherwise ensuring that your pilot light is set up for future success is a big part of a maintenance visit. Or at least it should be.

These visits will also help to maintain dozens of other parts and subsystems in your furnace.

If you live in Central Ohio, click the button below to contact us. We look forward to speaking with you!

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