8 Reasons Why Your Furnace Is Constantly Running

If your furnace runs constantly, you’ll quickly notice major problems with your home heating. A furnace that keeps running will keep your energy bills high, air quality low, and indoor environment inconsistent. So, let’s get to the bottom of your furnace issue and restore the cozy winter you deserve.

Your furnace repair experts at Total Comfort are here to answer all your questions, most importantly, “Why does my furnace keep running?” If you notice any of the following issues with your furnace, give our team a call today.

Table of Contents:

Why Does My Furnace Keep Running?

It may seem like a constantly running furnace is doing its job, but that’s not the case. A furnace that won’t shut off is likely malfunctioning, which can lead to various issues in your home. Here are eight possible reasons why your furnace is running nonstop.

1. Clogged or Dirty Furnace Filter

A clogged or dirty air filter can cause a range of problems for your furnace, and it’s one of the most common reasons a furnace runs non-stop. When the filter becomes clogged with dust, dirt, and debris, airflow is restricted, making it harder for the furnace to circulate warm air throughout your home. This forces the system to work overtime, running longer than necessary to maintain the desired temperature.

Solution: Furnace air filters should be changed about once a month to keep your furnace running efficiently. If you have pets, we recommend changing the filter more frequently, as pet hair and dander can quickly clog it, reducing airflow and efficiency. Neglecting to change the filter regularly can reduce efficiency, drive up energy costs, and shorten the lifespan of your furnace, so be sure to stay up to date with changes. To maximize efficiency and indoor air quality, consider upgrading to a high-quality pleated filter, which captures more dust, allergens, and debris while allowing better airflow.

2. Incorrect Thermostat Settings

Sometimes, the problem is as simple as your thermostat setting. If your thermostat is set too high, especially during freezing temperatures in Minneapolis, your furnace will struggle to keep up. The colder it is outside, the harder your furnace has to work to maintain comfortable indoor temperatures, which can cause it to run constantly and increase wear and tear.

Solution: We recommend keeping your thermostat set between 68-72°F during the winter months for optimal efficiency and comfort. Lowering the temperature can prevent your furnace from overworking, reduce the risk of breakdowns, and help keep energy bills in check. If you’re still experiencing issues, it may be time for a professional inspection.

3. Malfunctioning Blower Fan

A broken blower fan restricts airflow into and out of the furnace, reducing heating efficiency. If the motor’s bearings are worn out, the fan may slow down, become noisy, or struggle to operate, leading to uneven heating and increased energy costs.

Solution: Replacing the blower motor’s bearings can restore proper airflow, improve efficiency, and extend the lifespan of your furnace. If the issue persists, replacing the entire blower motor may be necessary to ensure consistent heating.

4. Dirty Gas Burners

Your furnace’s gas burners can become coated in dust and debris when inactive. This usually occurs in the summer, when there’s no need to use your furnace. Your furnace’s gas burners are likely dirty if they produce orange or yellow flames. A strong, healthy flame will be colored blue.

Solution: A professional furnace tune-up can help resolve this issue. We recommend scheduling furnace maintenance once a year, ideally in the fall or before the heating season begins. During a tune-up, a heating professional will thoroughly inspect and clean your furnace, ensuring all components are functioning properly and removing any debris that could block the gas burners.

5. Furnace Pilot Light Issues

Pilot lights are critical to igniting a furnace’s natural gas supply. Older gas furnaces always have a pilot light, which is the tiny blue flame at the bottom of your unit. Newer gas furnaces have a different pilot light design—these systems usually have an electric alternative that turns the pilot light on when necessary. An older furnace’s pilot light can go out because of dirty components, thermocouple problems, a low gas supply, or a faulty heat exchanger.

Solution: We recommend contacting furnace repair specialists when your pilot light goes out. This issue can be caused by a faulty component like a heat exchanger, which only professionals should attempt to fix. But you can still attempt to relight a pilot light on your own. If you want to give it a try, here’s what we suggest:

Read your furnace’s instruction manual for specific re-lighting steps and facts about your pilot light.
Find your furnace’s pilot light assembly and switch it from “pilot” to “off.”
Wait 5 to 10 minutes for excess gas to disappear from the combustion chamber.
Relight the pilot light by switching from “off” to “pilot.”
Hold down the furnace’s reset button and place a lit match or long lighter over the pilot light.
If the pilot light extinguishes again, contact a professional furnace repair crew.

6. Faulty Limit Switch

The limit switch serves multiple functions in your furnace, making it one of the system’s most important components. The thermostat and limit switch are in constant communication—when the desired temperature is reached, the limit switch shuts the furnace down. If the limit switch breaks, the blower motor won’t turn off. If the blower motor does not shut down, your furnace keeps running.

Solution: A faulty limit switch should usually be serviced by a furnace repair expert. But if you want to try resetting it yourself, give this method a try:

First, turn off your furnace by shutting off the heating switch on your circuit breaker.
Once your system is off, find the furnace control panel and remove it so you can see inside the furnace.
Find the limit switch (which should be a red, yellow, or white button) and press this button for three or four seconds before releasing.
Place the control panel back on your furnace and reactivate the heating switch on your circuit breaker.

7. Leaky or Poorly Insulated Ductwork

Damaged and poorly insulated ductwork fails to efficiently transfer heat. Air from your furnace will either leak out or cool down, forcing your system to work overtime to heat your home.

Solution: While temporary fixes like duct, mastic, or foil tape can address small leaks, long-term solutions require the expertise of an HVAC professional. They can inspect your ductwork and insulation, identify problems, and recommend the best system and ductwork solutions to ensure your home’s comfort.

Tips & Insights: Why is My Furnace Leaking Water?

8. Improperly Sized Furnace

Small furnaces often struggle to efficiently heat larger homes, leaving you with inconsistent temperatures and higher energy bills. A furnace installation expert can inspect your unit to determine whether it is properly sized.

Solution: If your furnace is too small, upgrading to a larger unit or adding a second furnace could be the answer. Alternatively, exploring ductless systems can help alleviate the strain on your existing furnace while keeping rooms at ideal temperatures and improving overall energy efficiency.

Why Is My Furnace Running Constantly in Cold Weather?

Extreme cold will force your furnace to activate more frequently, but it shouldn’t turn on and off every couple of minutes. This can wear your furnace down and increase your energy bills. A furnace should only cycle until your home has reached the thermostat’s listed temperature.

If your furnace keeps running in cold weather, there may be an issue with your furnace or insulation. Holes in insulation and ductwork can quietly cause excess heat loss. If you suspect something is wrong with your furnace or ductwork, we recommend contacting an HVAC expert immediately.

How Often Should My Furnace Cycle?

A healthy furnace usually activates 3 to 7 times per hour. But this number is different for each furnace and depends on outdoor temperatures. Other determining factors include:

Your furnace’s age.
The quality and quantity of insulation in your home.
The health and cleanliness of your ductwork.

When Should You Consider Replacing Your Furnace?

Struggling furnaces usually resume normal operation after a repair visit or yearly tune-up. But sometimes, repairing your furnace isn’t always the way to go. Here’s when you should opt for furnace replacement instead of repair:

Your Furnace is Old and Outdated: A properly maintained furnace usually lasts 10 to 15 years. When it crosses the 15-year mark, its efficiency is bound to be much lower than it was 10 years ago. Older furnaces are also costly to repair, sometimes being more expensive than a new installation.
Inconsistent Heating: If your furnace struggles to heat your home evenly, even after it has been repaired, it may be time for a new unit.
Yellow Flame: If your furnace’s flame is yellow instead of blue, it may emit dangerous carbon monoxide. You’ll want a furnace repair expert to inspect this issue and determine whether you need a new unit.
High Energy Bills: Older furnaces lose efficiency over time. A low-efficiency furnace has to work much harder than a high-efficiency furnace, leading to costly heating bills.
Banging and Screeching Noises: You should hear a gentle hum while your furnace is operating. If you hear bangs, booms, and screeches instead, a new unit may be necessary.

Tips & Insights: Gas Furnace vs Electric Furnace Installation

Need Furnace Repair or Replacement?

Total Comfort is your trusted partner for furnace repair and replacement in Minneapolis-St. Paul. We’ve been the Twin Cities’ go-to crew since 1956, offering superior service at an affordable price.

Minnesota winters are unpredictable and unforgiving, meaning your furnace can break down at any time. If your comfort and health are at risk after a furnace shutdown, lean on Total Comfort’s 24/7 emergency heating repair crew.

It’s cold out there, but we’re committed to keeping you warm. Contact Total Comfort when your furnace keeps running and you need solutions.