Beginners Guide To Troubleshooting Your Broken Furnace

Once the cool temperature starts to set in during the late and early months of the year, it is crucial to have a comfortable house to return home to.

A warm, pleasant home is imperative to overall peace of mind.

So what should you do when your (significantly expensive) furnace begins to dysfunction?

What are the tell-tale signs of a broken furnace, the remedies to solve each problem, and whether or not to repair or start from scratch and buy new?

In this Guide to Troubleshooting Your Broken Furnace, we take each problem one step at a time and list possible solutions to alleviate your anxiety.

Why Won’t My Furnace Turn ON?

The most obvious and significant clue that there is a malfunction with any type of machine is when it just will not turn on.

Thankfully, there are some quick and easy solutions you can check out first before you let stress creep into your mind.

Solution 1. Check the Thermostat 

Taking a look to make sure the thermostat is set properly is probably the easiest and most hassle-free solution you will find.

Reasons the thermostat is causing your furnace to not work could be:

  • The temperature you have set the thermostat isn’t high enough to encourage the furnace to kick on.
  • The actual setting on the thermostat is set to “cool” or “OFF” rather than “heat.”
  • Make sure the thermostat is located away from heat sources to prevent false readings. This could include direct sunlight, space heaters, and heating vents.
  • Check to see if the batteries are dead, in which case nothing would be signaling to your furnace to turn on.

Level of Difficulty: Easy DIY

Solution 2. Circuit Breaker Tripped

There is a chance that something caused your circuit breaker to trip.

Locate your circuit panel or fuse box and make sure to turn OFF, then ON your circuits or replace a possible blown fuse, respectively.

Also, there is a switch near your furnace that actually turns the furnace OFF and ON. Verify that no one accidentally flicked the switch thinking it could be connected to a basement or attic light.

Level of Difficulty: Easy DIY

Solution 3. Pilot Light/Ignition Problem

If you have an older furnace, it is likely your model has a standing pilot light.

If you have a higher efficiency, modern furnace, there is a good chance it uses a hot surface ignition to start your furnace.

Either way, it is possible a damaged or dirty pilot light/ignition is the cause for your furnace not working properly.

To observe the pilot light, remove the furnace cover panel with a screwdriver. If this is the first time attempting to use the furnace all year, and it is out completely, you can relight the pilot light.

Important Note: A successful pilot light will have a blue color to it. If it is more yellow or orange or tends to flicker, it is not burning properly and you may need to replace the pilot light altogether or contact a technician.

New models with ignitors have about a 5-6 year lifespan before they likely need to be replaced. You can call a technician to take out and replace your ignitor, but if you want to replace it yourself click here to see a step by step with tools necessary to do so.

Level of Difficulty: Medium DIY, Possible need for Technician

Why Does My Furnace Turn ON and OFF and Blow Cold Air?

It can be frustrating when the furnace is infrequent and distributes cool air.

There is a simple action you can take instead of wondering whether or not you need to completely replace your furnace.

Solution: Clean the Furnace’s Air Filter

The purpose of the air filter in your furnace is to reduce the contamination quality of the air blowing through your home.

Naturally, after time, your furnace’s air filter will become clogged with debris.

A dirty air filter will subsequently lead to:

  • Restricted air flow, therefore weaker and infrequent warm air
  • Your furnace needing to run longer than normal, which could cause it overheat and push out cold air
  • Poor overall indoor air quality
  • Your Furnace turning OFF and ON frequently
  • Ultimately, if the air filter is dirty enough, it could cause the entire system to shut down.

So what should you do?

Checking and replacing your air filter is a fairly simple process.

Simply turn off your furnace, locate the filter by confirming its whereabouts in the system manual or the company’s website, and replace it with a new filter.

Important note: If you’re unsure the quality of your air filter’s condition, an easy way to test the filter is by holding it up to the light. If you can’t see through it, there are too many dust particles attached and it is no longer able to function.

Level of Difficulty: Easy DIY

Why is My Furnace Continually Running?

Opposed to your furnace not turning ON, what should you do if you have difficulty turning your furnace OFF?

To some people, this may seem like a dream come true. A house that is constantly warm and toasty, just like the tropical vacation!

However, a gas bill will shatter that dream quickly.

Let’s look at a few simple and familiar approaches to take first.

Solution 1. Thermostat

Here we go again with that pesky thermostat.

The key component you want to look out for this time is to make sure you have the setting at “heat” and “auto” rather than “ON.”

The significant difference between the two is that the “auto” setting will have your furnace turn on based on the temperature settings you have established. The “ON” setting will just keep continually blasting your heat and holding your gas bill hostage.

Level of Difficulty: Easy, DIY

Solution 2. Verify Your Ducts Don’t Have Leaks

In this case, you’ll want to make sure your ductwork is intact and doesn’t leak anywhere.

Think about it this way, your house will never heat to its thermostat setting if all of your heat keeps accidentally spilling into your attic, right?

A leak in a duct can be detrimental to your overall dispersion of heat, but there is a way to solve the problem yourself. 

Important note: To easily spot where the duct is leaking and to tape it, make sure you check the ductwork while your furnace is running.

What you’ll want to do is carefully follow your ducts with HVAC tape and seal it where the heat is escaping.

Level of Difficulty: Medium, DIY

Solution 3. A Malfunctioning Limit Switch

Basically, the purpose of the limit switch in your furnace is to wait until your furnace is appropriately heated before sending out the warm air (to prohibit cool air from dispersing), and then once the heat cycle has ended, it shuts the fan and system off.

It can also act as a safety device in case the interior of your furnace begins overheating. In that case, it will cause the system to shut off automatically.

If your furnace and its fan are continually running, whether warm, cold, or no air is coming out, your limit switch could be broken or malfunctioning to the point of being unable to detect the end of the heat cycle and signal to shut down.

Another possibility is that your limit switch is set to “manual” rather than “auto.”

“Manual” will cause your furnace to run continuously where the “auto” setting will only have the furnace run during your predetermined heat cycles.

A white button on your limit switch will dictate whether or not your device is set to “manual” or “auto.”

If the device is correctly in its “auto” setting and still continues to run, you will have to replace or have a technician repair the limit switch.

Level of Difficulty: Medium, DIY and Potentially Need Technician

Why is There Water Around My Furnace?

When using your furnace, you may notice a small spot of water or maybe even a growing puddle.

Important note: Under no circumstance should you expect to see water coming from your furnace system. It is an immediate sign of malfunction.

There are various reasons your furnace could be leaking water, so we’ll break it up into two sections: 

  • DIY Solutions
  • Technician Solutions

Why is There Water Around My Furnace: DIY Solutions

Here are the most common reasons your furnace is leaking water that you can fix yourself.

  • The condensate pump has become unplugged
  • Moved drain line
  • Floor drain has become clogged with dirt and debris

If you own a condensing furnace, opposed to a conventional furnace, your system is actually supposed to conjure condensation. However, the most likely issues that you can fix yourself involve issues with how the condensation is drained.

You can diagnose whether the drain line has been bumped or moved from its floor drain location or the condensate pump is unplugged and fix these issues without the need for a repair technician.

Level of Difficulty: Easy, DIY

Why is There Water Around My Furnace: Technician Solutions

Conversely, here are reasons your furnace is leaking that you should lead you to get expert help.

  • Leaky Humidifier: This can be confused as a leak in your actual furnace. A clogged filter could cause the humidifier to begin leaking and it is best to have a technician diagnose properly.
  • A Clogged/faulty condensate pipe
  • Poorly designed exhaust pipe: In a conventional furnace, the exhaust pipe releases a combination of gases, like a car’s exhaust. However, if the pipe is broken or angled upward the flow of gas could be slowed or disrupted to the point where the gas cools and condenses to a liquid.

Level of Difficulty: Call a Technician

Why is My Furnace Making Weird Noises?

Even when your furnace is working properly, do you ever hear it rattling and banging?

Do you ever wonder whether if they are normal sounds or if something could be causing them?

Let’s go through some noises your furnace can make and what exactly those sounds may be foreshadowing:

  1. High-pitch squeal: If you hear a high-pitch emitting from your furnace, there is a good chance you have a belt issue. Sometimes the belt in your furnace can wear out and it could be as simple as needing some lubrication.
  2. Rattling: There are a few reasons your furnace may be rattling. The most common being gaps in your ductwork that you would need to seal and an imbalanced blower wheel.
  3. Boom/Banging: A loud banging or a boom is likely a build-up of gas in your furnace. This could end up causing the ignition to temporarily delay. Dirty burners delay the ignition and after the gas builds leading to the ignition a “boom” will occur.
  4. Clicking: If you hear your furnace click without it turning on, the noise could be a leaking gas valve. If your furnace clicks before the blower operates it could also mean a leaking gas valve or a cracked heat exchanger. 

Important note: A leaking gas valve could be releasing harmful carbon monoxide. Take immediate action by contacting a professional to fix the issue as soon as possible.

Level of Difficulty: Contact a Technician

Can Furnaces Cause Carbon Monoxide Leaks?

 As alluded to in the previous section, the answer to this question is a resounding yes!

Carbon monoxide is colorless, tasteless, and odorless.

It is toxic to humans and pets once your home reaches a sufficient level of saturation, and symptoms include:

  • Headaches
  • Dizziness
  • Nausea

How can this happen?

Your filters clean the air that circulates your home.

Dirty filters will lessen the quality of air in your home and may cause your furnace to struggle to pump out warm air.

Also, you want to make sure your home is properly ventilated so any negative excess gas (such as CO) can properly escape.

So what can you do to prevent this?

Unfortunately, in most cases, you will want to contact a professional technician to see what the correct underlying issue is causing the carbon monoxide leak.


You can purchase a carbon monoxide detector so that you won’t have to constantly worry about being on the hunt for the gas or misdiagnosing symptoms.

Level of Difficulty: Call a Technician, but pick up a CO Detector

Will Homeowners Insurance Cover a Broken Furnace?

So it’s been a few years, or so, since you’ve bought your furnace and all of a sudden on the coldest day of the year, it stops working.

The cold months are associated with expensive Holidays, such as Christmas, so you may be low on extra spending cash and wonder to yourself if your homeowners insurance will cover your furnace.

Unfortunately, despite most mortgage lenders requiring it, homeowners insurance tends to cover items destroyed by natural disasters or fires rather than normal wear, tear, and mechanical breakdown.

For instance, if your furnace is destroyed by a tornado or even if your furnace causes a fire to damage other items in your home, that will most likely be covered by your homeowners insurance.

A home warranty could potentially help with the cost of repairs. However, you should read through the home warranty carefully as they tend to have very specific requirements and exclusions.

So what is the best preventative action to take?

When planning to stay one step ahead of any future mechanical breakdown, the best option to stay prepared is purchase a warranty directly from the manufacturer or join your furnace manufacturer’s maintenance care plan.

It is still important to make sure the warranty covers wear and tear outside of external disasters, otherwise, the warranty is just as useful as your homeowners insurance that you likely already have.

What Are Some Good Furnace Maintenance Habits?

All this talk about furnace dysfunction can be a little stressful.

Perhaps you are someone who wants to make your devices, items, and machines last as long as possible.

You should!

So what actions can you take to maintain your furnace and keep it in tip-top shape?

1. Clean your air filters

Unlike the dust that collects, this tidbit of information isn’t going to disappear.

In every aspect of the well-being of your air quality and furnace system function, clean and operational air filters are a necessity.

Changing your air filters regularly will guarantee:

  • Better air quality
  • Lower energy bills
  • Reduced overall stress on your furnace

2. Clean the area around your furnace

This can include giving your furnace the space it needs from other objects and keeping the easy to get to parts clean.

For instance, if you look inside your furnace by the pilot light (you don’t have to specifically touch the pilot light as it is easy to break), you can wipe away any build-up of dust and debris.

3. Check your ductwork

This is more so lightly checking the efficiency of your ducts than inspecting a potential leak.

To make sure all is well, simply find your furnace and take a piece of toilet paper and hold it to each of your vents. 

If the paper moves, you have proper circulation. If not, refer to the section on ductwork gaps above.

4. Verify your smoke and carbon monoxide detectors are working

The most important action to take is to make sure these devices still work and the batteries have a sufficient amount of life left.

Peace of mind can go a long way here.

5. Confirm Thermostat functions

Before heat and cool air become what feels like a necessity, give each option a good test and make sure everything runs smoothly.

6. Hire a furnace maintenance technician seasonally

It is essential to take care of things that you can on your own, however, there is nothing wrong with hiring a professional maintenance technician to come at the beginning of Fall to give you a little expert advice on your current standing.

They will point you in the right direction and solve and concerns that may have been looming since the previous winter months.

Should I Repair or Replace My Furnace?

The answer is fairly obvious to owners of recent furnace purchases.

But what if the repair is significant and you’ve had the furnace for 10 years? What about 15 years?

Important note: Always take the age of your furnace into consideration when it comes to repairs. The older the furnace, the less likely you should pay for an expensive repair.

Also, newer furnaces tend to have higher efficiency. If you think about it, the money you spend on a new furnace is an investment in the long run when it comes to your gas bills.

Let’s break down optimal times to repair and the smartest times to replace.


  • Pieces such as limit switch, filters, drains
  • Wiring to/from your furnace system
  • If you are still under an efficient warranty that covers all/most of the repair costs


  • Heat exchanger fails
  • Control module malfunctions
  • Generally, if your furnace is over 15-18 years old (Especially regarding the pilot light)

What Are the Best Furnace Brands?

You’ve decided to either buy your first furnace or finally replace that old one making the noises that sound like a scary movie.

Where should you look first?

A quick peek at Consumer Report displays what they consider as the best brands.

The suggested manufacturers include:

  • Lennox
  • Carrier
  • Bryant
  • Rheem
  • Trane

Each furnace has its differences but since you will be acquiring a high-efficiency system that will save you money in the long term regarding energy and gas prices you can’t really go wrong with any of these top brands. Their retail prices range between $2,300 (Bryant and Rheem) and $3,000 (Trane).

Where Do We Go From Here?

Now you’re a little more aware of how your furnace functions and what possible signs you should look out for.

If your furnace problem fell under the DIY category, by all means, tackle that problem head-on and pat yourself on the back for being proactive about it.

However, if you have come to believe your best step forward is contacting a professional, don’t hesitate to schedule service by clicking the link below with our qualified and NATE certified HVAC repair technicians in the metro Atlanta area.

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