Furnace Troubleshooting: Common Heating Problems & Repairs

During the winter, your furnace helps ensure your family’s comfort and safety. But what can you do when your furnace isn’t adequately heating your home on a cold winter’s day?

While you can always call an HVAC service technician, sometimes you may have to wait a few days or more. And even if you bundle up in the meantime, the cold can still cause issues for your family and home.

At Fire & Ice, we get hundreds of service calls for furnaces each week during the winter months. So while you wait for your service appointment, let’s go through some common issues that can impact your furnace’s ability to heat your home.

A lot of articles on furnace troubleshooting focus on jargon-heavy issues that require a thorough understanding of HVAC. This isn’t one of those articles.

In this article, we focus on common factors that cause heating problems you can recognize just by living in your home.

This article may be able to help if:

• Your furnace isn’t providing enough heat
• Your furnace keeps turning on and off without running a full cycle
• Your furnace isn’t running

In some cases, you may be able to address these issues without the help of an HVAC service technician.

Your Furnace Isn’t Providing Enough Heat

When your furnace is running but isn’t providing enough heat, there may be an issue with airflow.

Your HVAC equipment’s primary job is to move air throughout your home. When there’s an issue with airflow, you may notice a significant temperature difference. But reduced airflow can damage your HVAC equipment if it isn’t addressed quickly.

Common issues that can affect your furnace’s performance:

1. Supply registers
2. Dirty furnace filter
3. Air duct dampers
4. Undersized furnace

Fortunately, many of these issues are fairly minor at this stage. You can even address a few of them without consulting an HVAC service technician.

Supply Registers

During the heating season, supply registers deliver warm air to the rooms throughout your home. Your supply registers may be located on the floor or in the ceiling.

If one room is colder than the rest of your home, check that the following are true:

1. The supply register isn’t covered or blocked
2. The vent on the register is open
3. When your furnace is running, air is coming from the vent

If the supply register is uncovered and open but airflow is still weak (or there’s no airflow at all), your supply registers likely aren’t to blame.

We’ll cover two more common heating issues that could be restricting airflow later in this article. But there’s another less common issue that’s worth mentioning here.

Over time, your ductwork can accumulate dirt, dust and other debris. And since heated air travels through your ductwork, the buildup of dirt in your ductwork can restrict airflow.

The National Air Duct Cleaners Association recommends having your ductwork cleaned every 3 to 5 years to promote good health and airflow.

For more information, check out this article that covers the best practices for ductwork cleaning.

Dirty Furnace Filter

Your furnace filter helps remove dirt and other debris from the air in your home year-round. This helps protect both your family’s health and your HVAC system.

But the more debris your filter removes from the air, the more it restricts airflow.

When your filter begins to significantly affect airflow throughout your system, you may notice three things:

1. It takes your furnace longer to warm up your home
2. Temperatures are uneven throughout your home
3. Weaker airflow coming from all supply registers

These can be the first signs that your filter needs to be changed. The longer a dirty filter remains in your system, the dirtier it will get. This will lead to more serious problems, which we’ll discuss later in this article.

I can’t stress enough how important it is to change your furnace’s filter regularly. Dirty and clogged filters are the number one cause of airflow issues.

How often your filter should be changed depends on the type of filter and your home. One-inch filters typically need to be changed every 30 days (or less). Meanwhile, some four-inch filters can last up to a year without being changed. Your filter’s packaging should include additional information on when you should change it.

You may need to change your filter sooner if:

• You live in an area with a lot of dust or construction
• You have indoor pets that shed or molt
• You frequently light candles

While these are the most common factors we see here in Central Ohio, there may be additional factors depending on your home. For best results, monitor your system’s performance. If you notice some of the issues above, check your filter.

For more information, check out this article that breaks down how, why, and when you should change your filter.

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Air Duct Dampers

Like your supply registers, air duct dampers allow you to adjust how air moves to specific areas of your home. But your system’s dampers are located close to your furnace.

Dampers are typically set differently for the heating and cooling seasons. These settings can help compensate for seasonal changes. If you notice that part of your home seems chilly, your dampers may not be positioned for the heating season.

You can reposition your dampers yourself. But repositioning your dampers can involve a lot of trial and error if you’ve never done it before.

If you aren’t comfortable adjusting the dampers yourself, an HVAC service technician can help. Ask your technician to adjust your dampers for winter during your furnace’s annual tune-up.

Undersized Furnace

While undersized equipment doesn’t always affect airflow, it can hurt your furnace’s performance.

In this case, an undersized furnace refers to a furnace that isn’t powerful enough to adequately heat your home.

When your furnace is too small for your home, it’ll run more often than it should in an attempt to heat your home. But despite running frequently, an undersized furnace won’t be able to adequately heat your home.

If your furnace is undersized, you may notice:

• Uneven temperatures throughout your home
• Upper floors and rooms farthest from your system remain cold

While oversized equipment tends to be more common, undersized equipment is still too common here in Central Ohio and throughout the country. (We’ll talk about oversized furnaces later in this article.)

Your Furnace Keeps Turning On & Off

When your furnace turns on and off without running a complete heating cycle, we call this short cycling.

If your furnace is short cycling due to ignition issues, your furnace may attempt to start three times without running. In newer furnaces, this typically results in a soft lockout. The furnace will go through this process two more times.

After the final attempt, a newer furnace will enter a hard lockout, which only an HVAC service technician can address.

But older furnaces may go into a hard lockout after the first three attempts to ignite.

When your furnace enters a lockout, it won’t produce heat. But if an issue doesn’t trigger a safety feature, it may produce heat even while short cycling.

Common issues that cause short cycling:

1. Dirty furnace filter
2. Dirty flame sensor
3. Dirty burners
4. Oversized furnace

Dirty Furnace Filter

When your furnace begins short cycling, this can be a warning sign that your furnace is overheating.

In the previous section, we discussed how dirty furnace filters can affect your furnace’s performance by restricting airflow. With enough airflow restriction, your furnace will overheat.

Overheating can majorly affect your furnace’s life expectancy. If left unchecked, overheating can damage your furnace’s components, like the heat exchanger, a metal part that heats the air that circulates throughout your home. Heat exchangers can cost as much as $3,500 to replace.

Overheating can also damage your furnace’s safety features, like limit switches. Limit switches shut down your furnace when it overheats. But limit switches can also get stuck if your furnace overheats.

Dirty Flame Sensor

A flame sensor is a safety feature that turns off the gas if your furnace’s burners don’t light. This ensures that gas doesn’t fill your furnace cabinet.

But because a flame sensor sits in open flames from the burners, it accumulates soot over time. If the flame sensor isn’t cleaned off, eventually it won’t recognize whether the burners are lit or not.

Luckily, this tends to be a quick fix. Your HVAC service technician should be able to clean off a dirty flame sensor quickly.

Your HVAC service technician should also clean your flame sensor during your annual furnace tune-up. This helps ensure that you don’t get stuck without heat on a cold day.

But as easy as this fix is, I recommend leaving the flame sensor cleaning to a professional. Flame sensors must be positioned at a specific angle. Otherwise, your furnace will continue to kick on and off without heating your home.

Dirty Burners

Your furnace’s burners help channel the open flames that heat your home.

Like flame sensors, burners can accumulate soot over time. This soot can clog the burners. When the burners don’t light, the flame sensor turns the furnace off. 

Also like flame sensors, your HVAC service technician can address dirty burners by cleaning them.

Oversized Furnace

Oversized equipment may not experience lockouts. But if your furnace is oversized, it likely won’t run a full heating cycle.

In this case, an oversized furnace refers to a furnace that’s too powerful for your home.

Outside of HVAC equipment, we tend to favor bigger and more powerful options. But the size of your HVAC equipment isn’t an option. To get the most out of your system, your HVAC equipment must be the right size.

If your furnace isn’t the right size for your home, you’ll lose out on more than just comfort. You may need to replace an improperly sized furnace as much as 10-15 years sooner than an accurately sized furnace.

To make sure you get the most out of your furnace, check out this article that breaks down how your HVAC partner should size your HVAC equipment.

Your Furnace Isn’t Running

There are few things quite as worrisome as a furnace that stops running during winter, especially if your furnace quits during a time when HVAC service technicians are in high demand. I mean, HVAC equipment always seems to break down when you need it the most, right?

There’s a reason for that. If your furnace is under strain, it’s already working hard to heat your home. But during cold snaps, a strained furnace has to work even harder.

But there are small issues that can cause your furnace to shut down. You may be able to address some of these yourself and turn the heat back on much more quickly.

Common heating issues that can prevent your furnace from running:

1. Thermostat settings
2. Dirty furnace filter
3. Tripped breaker
4. Malfunctioning igniter

Thermostat Settings

Your thermostat settings aren’t always to blame, of course. But if you have to wait a few days for a technician, it can help to check some of the factors you can control.

Thermostat troubleshooting checklist:

• Make sure your thermostat is switched to “heat,” especially if it’s early in the heating season.
• If your thermostat has batteries, try replacing the batteries.
• If you have a wifi thermostat, make sure it’s connected to the internet. If your thermostat won’t connect, you may need to restart your router.

Dirty Furnace Filter

In previous sections, we’ve talked about minor symptoms and warning signs that your furnace filter needs to be changed. If left unchecked for long enough, a dirty furnace filter can leave you without heat entirely.

In the previous section, we talked about how a dirty furnace filter can cause your furnace to overheat and short cycle. Eventually, this can trigger a hard lockout if your furnace doesn’t have adequate airflow. And as we discussed earlier, only your HVAC service technician can unlock your furnace after a hard lockout.

If your furnace stops running due to a dirty filter, your service technician should also check on the condition of your furnace’s components.

Tripped Breaker

Sometimes your furnace can trip your circuit breaker. While you can reset the breaker, chances are that it will happen again. A service technician will likely need to take a look at your system.

One reason your furnace may trip a breaker is due to a strained blower motor, a component that’s responsible for circulating air throughout your home.

Your blower motor can become strained due to a few factors, including:

1. Reduced airflow throughout the system. Dirty furnace filters and closed or blocked registers can subject your blower motor to strain. You can address these by regularly changing your furnace filter and checking your registers (which we discussed earlier in this article).
2. Debris buildup on the blower fan. Like your furnace filter, your blower fan can accumulate dirt, pet hair and other debris over time. Your HVAC service technician can address this by deep-cleaning your blower fan.

Malfunctioning Igniter

Your furnace’s igniter provides the spark that heats your home. But your igniter can wear out over time.

Many modern igniters can last between 10-20 years (depending on the type of igniter).

Fortunately, your HVAC technician should be able to replace your igniter quickly.

How Improper Installation Affects Your Comfort

An improper installation sets your furnace up to fail from the beginning.

Your HVAC partner should install your furnace according to manufacturer specifications and local building codes. This helps set up your furnace to operate safely and efficiently.

Choosing an HVAC contractor that follows industry best practices is the best way to ensure that your HVAC equipment is installed properly.

According to these best practices, your HVAC contractor should perform a load calculation and pull permits before they install your new HVAC equipment.

Permits are required by law. But on top of covering you legally, permits also help ensure your safety. Once your HVAC contractor installs your equipment, a third-party inspector checks that the installation complies with local building codes and manufacturer specifications.

For everything you need to know about your furnace – from installation to daily function to routine maintenance – check out our guide to home furnaces.

Three Steps that Help Prevent Common Heating Problems

Unfortunately, you likely won’t be able to completely avoid furnace repairs or heating problems. But you do have the power to prevent them for as long as possible.

Three steps that help prevent common heating problems:

1. Change your filter regularly
2. Schedule a furnace tune-up every year
3. Choose an HVAC contractor that follows industry best practices

These steps can help you get the most out of your HVAC equipment, especially when combined.

If you’re looking for an HVAC company to help protect your system, we’d love to speak with you!

At Fire & Ice, we’re dedicated to your comfort and your HVAC system. We have skilled service technicians and knowledgeable comfort specialists on staff to help you customize your HVAC system. And all of our employees take the time to understand your needs and thoroughly explain all possible solutions.

To schedule a service appointment for your furnace, enter your zip code below.