Eight Warning Signs That Your Furnace May Be Failing

A furnace is a machine that produces the heat in your house’s central heating system, and it is responsible for distributing warmth around your home when needed. It is a must-have feature in every home, but unfortunately, it also has a lifespan. On average, a furnace can last for approximately 15 to 20 years, but only if maintained well. If not properly taken care of, it will experience a faster decline in service and performance.

The earlier you see signs of deterioration, the faster you can save or fix your furnace. Unfortunately, sometimes the signs that your furnace is failing are not easy to see. Determining the real condition will require close attention and keen observation, especially for a homeowner with no experience working on furnaces. 

If you are curious about your furnace’s condition and want to watch out for its condition, here are some signs you should look for:

1: On and Off-Cycle

One of the most evident signs that there is something wrong with your furnace is when it starts and stops on its own. This situation can be due to many reasons. For instance, it can happen because something is blocking the system. When there is a blockage, the system cannot complete its heating cycle, causing your furnace to turn on and off. Another possibility is that the furnace’s fan motor is slowly dying or full of dirt. To know the real cause behind this problem, it is best to consult with a professional furnace technician.

2: Yellow Flames

Another easy-to-spot sign is the color of your furnace’s flame. Typically, using natural gas will make the flames look almost completely blue. If you have a roaring blue flame with a light blue triangle in the middle, that means the burner and fuel are working as they should. However, if you see yellow flames, that is an indication that you have a dirty burner or that the gas is not correctly burning. 

3: Moisture Buildup Around the House

When there is a problem with your furnace’s vents, it can result in damp and stagnant air around the house. When there is not enough airflow throughout the house, moisture spots can develop on different surfaces, leading to other home and health problems. However, moisture spots can be an effect of many conditions. To make sure that it is because of your furnace, remember to inspect your furnace regularly. 

4: Increase in Energy Bills

You will know that one of your house appliances is not properly working if you notice that your bills suddenly increase without changing your lifestyle or usage. Similar to an air conditioner unit during the hot season, your furnace will work harder when the weather is cold. However, if the temperature is not too hot or too cold, but your furnace is working harder than normal, you need to have it checked. 

Sometimes a dirty furnace can lead to this situation. To make sure that there is no other problem apart from filth and grime, replace or clean your filter as often as needed. If you do this, and the furnace still performs the same, it is time for a more in-depth inspection. 

5: Rusted Flue 

The flue refers to the duct, pipe, or chimney opening responsible for exhausting gas from your furnace. If you notice that your furnace flue is starting to rust, do something about it. Rust means that there is a leak somewhere around your house.

This problem can lead to carbon monoxide poisoning inside your home. When there is corrosion in your furnace’s flue, it will hinder your flue’s performance, and one of its essential tasks is to let out these harmful gases from your house. 

6: Old Unit

As mentioned above, a furnace can function for up to 20 years, but this might not always be the case. No matter how much you care for the machine, it will eventually wear out and start to perform poorly.

If you have been using your furnace for more than a decade, you may start considering replacing your unit with a new one. While your goal is to maximize its use, your furnace can only do so much. Eventually, you will want a better system that can perform well and help you save on expenses better.

7: Water Puddles Surrounding Your Furnace

Do not immediately panic if you see water puddles around your furnace. These are a usual sight that indicates your machine is working. In fact, the same thing happens to your air conditioner. Instead of panicking, what you should do is determine where the water is coming from. Here are two scenarios that can occur and the recommended next steps:

  • You see water puddles only when running your AC: If this is the case, it could mean that there is a leak or clog in your water condensate line. This problem has an easy fix.
  • You see water puddles coming directly from the furnace: This situation could mean something more serious is happening with your furnace. Make sure to contact a professional technician to check on your furnace’s condition.

8: Problematic Thermostat

Sometimes, a thermostat that continuously adjusts, no matter how many times you fix it, could indicate a problem. One of the potential issues is a malfunctioning furnace. When a furnace can no longer meet the house’s needs, it will start to fluctuate, affecting the performance of your thermostat. However, the constant adaptation of the thermostat could also mean that you need a new thermostat. Consulting with an expert can help you determine the precise reason. 


Furnaces are not easy to understand for many homeowners. Knowing if yours has a problem will require extensive knowledge, keen eyes, and enough experience. However, that does not mean you should ignore the machine completely. There are silent signs that can tell you something is wrong with your appliance. These eight symptoms can be significant indicators. As a sure way to check on the real condition, you can always seek the help of a professional furnace technician. 

Contact a trusted technician as soon as you need furnace repairs. If a repair is no longer an option, replace your unit as soon as you can. Whatever furnace service you need, we can help. Air Unlimited Heating & Cooling is an EPA-certified and ENERGY STAR-certified business that can help you with your heating and cooling needs 24/7. Contact us today to book a service.