5 Warning Signs Your Furnace Needs Service or Repairs

Does your furnace run the way it used to? Sometimes it can be difficult to put your finger on what changed (or when it changed).

These changes can be subtle at first. You may notice a change in airflow from some of your registers. Maybe your furnace is running longer or not as long as normally did. You may even notice new sounds, smells and pools of water coming from your furnace.

These changes can indicate that your furnace needs service or repairs.

I’ve worked in HVAC service for a little over 15 years. And while I could list the performance benchmarks that I look for as an HVAC professional, that list likely wouldn’t help many homeowners. After all, HVAC service technicians have a variety of tools that can help them diagnose an issue with your furnace.

So instead, this article focuses on the changes that you might notice just by living in your home.

In this article, we discuss five of the most common changes in your furnace’s performance that you may notice. We also discuss some of the issues that cause these changes.

Signs Your Furnace Needs Repaired

In this section, we’ll break down the following signs and what can cause them:

• Changes in airflow
• Short cycling (kicking on and off without running)
• Abnormally long runtime
• Abnormal sounds and smells
• Puddles of water and leaks

Changes in Airflow

When you get down to it, your HVAC system has one job: move air.

Your furnace could run constantly, but without proper airflow throughout your furnace and ductwork, it wouldn’t be able to heat your home evenly or efficiently.

Over time, you may notice changes in airflow. Maybe one vent has a noticeably weaker airflow than before. Maybe one room is colder, hotter or more humid than it used to be depending on the time of year.

And while it may be easy to put on more layers or avoid those spaces altogether, decreased airflow can lead to significant issues and expensive repairs in the long run.

Factors that affect airflow:

• Dirty filter. Your filter’s job is to keep the air in your home clean. But the more dirt and other debris your filter collects, the more it restricts airflow throughout your home. You don’t necessarily need an HVAC service technician to change your filter. But many of the service calls we go on are due to dirty filters. So if you’re having issues with airflow, check your filter first. (This isn’t the last time you’ll hear about dirty filters in this article. Dirty filters can also contribute to other issues. We’ll talk about some of these other issues two more times in this article.)
• Air duct dampers. Dampers allow you to manually adjust the amount of air that goes to specific rooms or areas of your home. While this can offer more control over the temperatures in these rooms, you may need to adjust these dampers to allow for adequate heating or cooling. Your HVAC service technician can help adjust your dampers, but this is also something you can do yourself.
• Clogged blower fan. Your blower fan helps circulate air throughout your home. But over time, debris like pet hair and dust can clog your blower fan. This can decrease airflow throughout your home and increase strain on your blower motor, which operates the fan. Your HVAC service technician can solve this by deep-cleaning your blower fan.
• Leaky ductwork. Once your furnace produces heat, your ductwork helps distribute that heat throughout your home. But your ductwork can degrade over time. In some cases, your HVAC partner may need to reseal, repair or replace sections of your ductwork.

Short Cycling Furnace

When your furnace kicks on and off without running a full cycle, this is what we call short cycling.

If your furnace only recently began short cycling, short cycling can indicate several different issues, including:

• Dirty flame sensor. A flame sensor ensures that your furnace’s gas valve shuts off if your burners don’t light. To do this, the flame sensor sits in the open flames from the burners. Over a year, the flame sensor can collect soot. Eventually, your flame sensor won’t be able to tell when the burners are lit or not, which leads to short cycling. Your HVAC technician can usually address this by cleaning your flame sensor.
• Dirty burners. Like your flame sensor, your burners can accumulate soot over time. In some cases, this soot can clog your burners, which prevents them from lighting. As a result, the flame sensor shuts down the gas valve. Then your furnace short cycles as it attempts to heat your home.
• Malfunctioning ignitor. In some cases, your ignitor can be the issue. Your furnace’s ignitor provides the spark that heats your home. And without that spark, your furnace will short cycle as your flame sensor registers that the burners aren’t lit.
• Dirty filter. Since dirty and clogged filters limit airflow, your furnace can overheat. And because of safety features like limit switches, your furnace kicks off until it cools down. While this can leave you without adequate heat, dirty filters can lead to more significant long-term issues. We’ll discuss the worst-case consequence in the next section.

Another common cause of short cycling is improper sizing.

To meet your heating and cooling needs, your HVAC equipment must have the right output to heat and cool your home. We refer to this output as a furnace, air conditioner or heat pump’s size.

If your furnace is too big for your home, its heating output will be too powerful for your home. As an oversized furnace struggles not to overheat your home, it’ll short cycle.

An oversized furnace can affect your comfort – and your wallet. Improper sizing for HVAC equipment can lead to frequent repairs and premature replacement. (We’ll discuss another consequence of improper sizing in the next section.)

Abnormally Long Furnace Runtime

In some cases, HVAC equipment with a longer runtime can benefit you. But if your existing furnace begins to run longer than it did in heating seasons past, this could be a sign of a few issues.

Some of the issues that cause abnormally long runtimes include:

• Dirt buildup on the heat exchanger. Your heat exchanger is a metal component that helps heat the air that circulates throughout your home. Over time, the heat exchanger can accumulate dirt, soot and other debris. This means that your furnace has to work harder and run longer to heat your home. But your HVAC technician can address this by cleaning your heat exchanger.
• Cracked or malfunctioning heat exchanger. When your system has to work harder (whether because of dirt buildup or dirty filters), parts eventually begin to break down. For heat exchangers, this can mean cracks, corrosion or other issues. Cracked or otherwise damaged heat exchangers have to work harder and run longer to heat your home. But cracked heat exchangers can lead to complete system breakdowns eventually.

Heat exchangers can cost thousands of dollars to replace once they sustain damage. Fortunately, many furnace manufacturers offer lifetime warranties on their furnaces’ heat exchangers.

However, these warranties require regular HVAC maintenance. If your HVAC system hasn’t been maintained, your furnace’s manufacturer may not cover the cost of a replacement heat exchanger.

And without a warranty, heat exchangers can cost as much as $3,500 to replace. That’s as much as a brand new furnace.

A damaged heat exchanger is the worst-case scenario. And while it’s not always inevitable, you can decrease the risks. We’ll discuss this more in-depth later in the article.

As promised in the last section, let’s talk about how improper sizing can lead to longer runtimes.

So you know that your furnace will short cycle if it’s too large for your home. But if your furnace is too small for your home, it won’t have the power it needs to heat your home. This means that an undersized furnace will run much longer than it should in an effort to heat your home.

And because an undersized furnace works much harder and runs much longer than properly-sized equipment, it can also require frequent repairs.

We’ve only scratched the surface on sizing, though. This article breaks down the sizing process for HVAC equipment.

Abnormal Smells and Sounds from Furnace

There are only a few instances when a furnace may emit abnormal smells or sounds. And these instances are fairly rare.

Sounds and smells to look out for from your furnace:

• The smell of rotten eggs (gas). Natural gas furnaces are one of the most popular options both here in Central Ohio and throughout the country. Natural gas is normally colorless and odorless. But gas companies add a substance that smells like sulfur or rotten eggs to natural gas. This can help alert you to gas leaks. (There are other signs of gas leaks too. Learn more about all the signs of a gas leak here.) If you smell rotten eggs at home, leave your home and call 911. Columbia Gas customers can follow these steps to report a gas leak.
• The smell of something burning. If you notice a burning smell coming from your furnace, there are two possible causes. The first is dirt buildup on your heat exchanger, which we discussed in the previous section. The second is an overheated blower motor. Your blower motor can overheat if your filter is dirty or clogged.
• A slow and noisy fan startup. If you hear something like this wobbling sound effect when your furnace starts up, there could be an issue with your blower motor’s bearings. The bearings need lubrication in order for the blower motor to work properly. Over time (and with overheating), this lubrication can dry out. In some cases, your HVAC service technician may be able to lubricate the blower motor. But this isn’t always possible with some types of blower motors. Regardless, your service technician should be able to help with this.

Water Near Your Furnace

If you notice water leaking from your HVAC system, you should contact your HVAC partner immediately. Water can also damage your furnace’s circuit board and other components, which could lead to more costly repairs.

Pools of water and leaks can indicate a few issues, including:

1. A damaged heat exchanger
2. A compromised seal on your evaporator coil

If you notice water pooling near your high-efficiency furnace during the winter, your heat exchanger could be damaged. This is only an issue for oversized high-efficiency furnaces.

Most high-efficiency furnaces have two heat exchangers. The secondary heat exchanger helps these furnaces conserve heat that standard efficiency furnaces release in the form of waste gases.

As we discussed earlier, an oversized furnace will short cycle. But when an oversized high-efficiency furnace short cycles, water vapor can condense inside the secondary heat exchanger. And since an oversized furnace won’t run as long as it should (by manufacturer specifications), the water stays in the secondary heat exchanger.

Over time, this can lead to cracking, rusting and corrosion, which affects your furnace’s efficiency. And if the secondary heat exchanger cracks, you may notice water coming from your furnace.

If you notice water near your furnace during the summer, the seal on your evaporator coil could be compromised.

Your evaporator coil is the indoor component of your air conditioner or heat pump. In some HVAC setups, the evaporator coil is located on top of your furnace cabinet.

Your evaporator coil naturally produces moisture – that’s why your air conditioner/heat pump has a drain. But if your evaporator coil isn’t properly sealed, this moisture could leak onto and around your furnace.

Your HVAC partner should be able to evaluate the seal and ensure that your furnace isn’t damaged.

How Much Does a Furnace Repair Cost?

The cost of a furnace repair typically depends on the cost of the replacement part. And the cost of a part can depend on its complexity and brand.

For more information, check out this article that breaks down how much you can expect to pay for each replacement part.

The Best Way to Prevent Furnace Repairs

Many furnaces have a life expectancy of 15-20 years. And chances are that you’ll need at least one repair for your furnace in that time.

You can never totally avoid furnace repairs. But you do have the power to prevent them as much as possible.

Prevent damage to your heat exchanger with two steps:

1. Change your HVAC system’s filter. How often you need to change your filter depends on the type of filter you have. Learn more about your furnace’s filter and how to change it in this article.
2. Schedule regular maintenance. An annual tune-up can ensure that your furnace is prepared to heat your home. And during an annual tune-up, your HVAC service technician can catch issues before they leave you without heat on the coldest day of the year. Learn more about what you can expect during a furnace tune-up in this article.

If you’re a Central Ohio resident and you need furnace service or maintenance, we’re here to help.

When you understand more about your HVAC system, you can make the best decision for your family and home. At Fire & Ice, our service technicians take the time to explain the condition of your furnace without pressuring you to make a certain decision.

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