When it’s cold outside and the snow is up to your windows, the last thing you want is a malfunctioning furnace. Of course, there are the common furnace issues such as a blown out pilot light, but what happens when it stops working properly, or just stops working all together?

From leaking water to a constantly running furnace, there are plenty of reasons to question what’s causing your furnace problems. But luckily for you, we’ve been around the block a few times to know what’s causing your furnace to act up and how to fix it.

If you have furnace repair questions about your system’s latest behavior, we have the answers for you down below.

1. Why Is My Furnace Leaking Water?

Have you ever gone to change a dirty filter and found a puddle of water around your furnace? Is it a furnace issue or something else? 

There could be a couple culprits. However, in our experience, the most common reason furnaces start to leak water is due to a condensation leak.

High-efficiency furnaces have cool exhausts, meaning they produce condensation. Because of this, these furnaces are installed and channeled to a floor drain. The leak most often occurs when the condensation tubing becomes clogged or has a break in the line. Or, your floor drain is clogged and the water simply has nowhere to go.

If you don’t have a high-efficiency furnace, but you’re still seeing a water leak, there are a few more potential causes:

• A faulty secondary heat exchanger
• A faulty furnace humidifier
• A clogged internal drain

All three of those issues can be costly to fix, but you’ll want to call in a professional for a furnace repair. In each scenario, water could be leaking inside your furnace doing plenty of damage to your system and potentially leading to downtime (Brrr).

2. Why Does My Furnace Keep Turning Off?

This furnace repair question is probably the one we get asked the most. But luckily, it’s typically a pretty simple fix. In fact, it’s usually a fix you can do all on your own, without needing to call in the experts.

The most common reason furnaces “short cycle,” or turn on and off frequently, is due to a dirty air filter. Dirty furnace air filters restrict and clog air from reaching your heat exchanger, which causes your furnace to overheat and shut down. So, if you haven’t replaced your filter yet this month, chances are you just need to put in a fresh filter.

Already replaced your filter and aren’t seeing a difference? Is your furnace not producing enough heat? Check your thermostat. It may be that your thermostat is placed near a heat source like sunlight, heat register, or fireplace. This causes the thermostat to think your home is warmer than it is, triggering the furnace to turn off early and often.

The last possible cause of short cycling is that your furnace hasn’t been sized correctly for your home. A furnace that is too large for your home heats the area too quickly and shuts off. Then, once your home cools off the cycle repeats. This is the most costly issue as the solution would be to replace your furnace.  

3. How Do I Light the Pilot Light on a Furnace?

In the event that your furnace pilot light goes out, here’s how you can get it lit again:

1. Read the instructions label on your furnace.
2. Find the pilot light and components.
3. Turn the pilot dial to the “off” position.
4. Wait at least five minutes to give the gas time to dissipate.
5. Turn the pilot dial to “pilot.”
6. Hold down the “reset” button next to the dial and bring the flame of your lighter close to the pilot light opening.
7. Release the “reset” button.

Now, your furnace pilot should be lit and ready for action.

4. Why Is My Furnace Blowing Cold Air?

When a furnace starts to blow cold air, it’s easy to get concerned. After all, you want heat, not cold.

The first place we recommend you investigate is your furnace’s fan setting. If your fan is set to “on” your furnace blower is running even when the furnace isn’t producing warm air. To correct this, change the fan setting to “auto.” This ensures that the blower only runs when the furnace is actively heating the air.

The next common cause of cold air from your furnace is one we’ve already talked about in one of the questions above: the air filter. Dirty air filters are often to blame because they restrict airflow to the furnace’s heat exchanger, causing your furnace to shut down and cold air to build up. Just replace your air filter and you should start to feel warm air filling up your home.

Finally, check your pilot light. If the pilot goes out, your furnace is trying to run without a heat source. To get the light lit again, see the question above.

5. Why Does My Furnace Keep Running?

Most often, furnaces run constantly because the thermostat fan setting is turned to “on.” To correct this, change the setting to “auto” and turn the thermostat to a temperature that’s lower than the current room temperature. You should start to hear the furnace cycling after five minutes or so.

If the furnace still isn’t cycling, there could be one of three problems happening:

• The fan limit switch is set to “manual override”
• You have a faulty fan limit switch
• Your thermostat isn’t wired properly

Before you call in a heating professional, make sure your fan isn’t set to manual override. The fan limit switch is typically located inside the furnace panel cover in the upper right-hand corner. Once you’ve located the switch, make sure the small white button is not pressed in. If the button is pressed in, the switch is set to manual, overriding your thermostat setting and forcing the fan to run constantly. Reset the switch to automatic by pulling on the button.

If you’ve reset the switch to automatic and are still hearing the system run, it’s time to call the experts as a larger issue is occurring.

6. Why Is My Furnace so Loud?

From rattling to screeching, there are plenty of noises your furnace can make. And almost all of them leave you wondering if there’s something wrong with your furnace.

If your furnace is making loud, questionable noises there are a number of potential causes, including:

• Improper blower assembly
• Expanding ductwork
• Loose debris or screws
• Leaky ductwork
• Bad belt or motor bearing

For a full list of potential noises and how to silence them, check out our guide to common HVAC noises.

7. Why Does My Furnace Smell?

Rotten eggs. Burning wax. Dust. There are a number of smells your furnace can produce. And none of them are pleasant.

If your furnace has an unusual odor to it, the most common causes are:

• The furnace hasn’t been used in a while
• Your air filter is clogged
• There’s a natural gas leak
• Your furnace parts are overheating

Without question, the most serious issue on this list is a natural gas leak. So, if you’re smelling rotten eggs near your furnace (not your fridge) turn off your furnace, open your home’s windows, leave your home immediately, and call your utility company.

What other steps should you take in the event of funny smells? Read our guide on common furnace smells and what to do about them.

We’re Here to Help

Furnaces are serious appliances. Some common furnace problems are easy to fix, but don’t forget that your furnace can experience serious problems, as well. If you have any questions that weren’t included in the list above, we want to answer them for you. Leave a comment below or contact us and we’ll calm any concerns you may have.

Did the answers above uncover any problems with your furnace? If you need professional help to kick your furnace back in gear, schedule a furnace repair visit with us by giving us a call at 612-825-6867 or submitting a service request.

P.S. Our phone lines are open 24/7 over the winter season in case of emergencies!