2023 Homeowners Guide to DIY Furnace Repair: 16 Most Common Problems & Solutions

homeowners guide to furnace repair

❄️ The Season of Furnace Repairs

You had a great summertime, enjoying all that warm weather. But now you’re in Fall, and Winter is looming.

October and November bring out all the pretty colors, but now many Canadian provinces and the Northern US probably have had a significant snowfall under their belts.

So it’s officially the heating season for homeowners

What’s that mean: Furnace Repair.

For many people, turning on their furnaces for the first time in a while comes with a feeling of apprehension.

Will it work correctly, or will you have to fork out a costly malfunctioning furnace repair job?

PRO TIP: Read This Beginner’s Guide! 

Even if you’ve never seen the inside of a furnace, you can troubleshoot and take care of any furnace repairs yourself.

This guide walks you through common questions we hear about furnace issues and their solutions. 

Once you’ve spent some time getting to know your furnace, you can decide if you want to repair it, call in an HVAC professional, or invest in a new heating and cooling system.

Remember, the biggest furnace repair cost usually relates to the heat exchanger, the furnace blower motor, the circuit board, the draft inducer motor, or the gas valve.

While the least expensive furnace repairs are the furnace’s flame sensor, the electric ignition module, the thermostat, the high limit switch, the rollout switch, the circuit breaker and the furnace filter.

Most of these furnace failures could have been prevented by performing annual furnace maintenance or by having a professional HVAC contractor perform an annual furnace tune-up.

🛑 SAFETY FIRST: If you feel uncomfortable performing any DIY furnace repair, you should call your local furnace repair professional.

1. The Dirtiest Furnace Filter in Town

changing out a Furnace filter
The first stop for a furnace repair is a dirty air filter

You can’t write a furnace repair guide without giving a shout-out to air filters.

Think of the air filter as the gatekeeper for your furnace.

It traps dust, pet dander, and other nasty debris you don’t want circulating inside your home. You also don’t want these things inside your furnace.

Changing your furnace filter is an essential part of getting your furnace inspected.

Clogged filters result in reduced airflow. Reduced airflow makes your furnace work harder.

Overworking your furnace usually means you pay for more repairs. 

Also, reduced air flow in your furnace can cause your heat exchanger to overheat and shut off your furnace.

A blocked air filter can also cause a condition called short cycling.

If the system doesn’t have enough airflow, it will run until the high-limit switch trips it off.

Your system will reset and run again until it trips.

Related Reading: Furnace Short Cycling: 9 Causes and Solutions

You may not have the dirtiest air filter in town, but just do it if you haven’t changed it since the beginning of summer.

While it’s not precisely a furnace repair problem, not changing air filters can cause excessive wear and tear on your heating system.

This also leads to a reduction in indoor air quality.

If you would like to know more about your filter and how it protects your indoor air quality, we have a great guide on it right here: Air Filter Guide. What MERV Rating should I use for my home?

2. Inspect and Clean the Flame Sensor

Furnace Flame Sensor
A Furnace Flame Sensor

The flame sensor ensures that the gas valve doesn’t continue to pour gas into your propane or natural gas furnace without a flame present.

As the flame sensor sits in the flame the entire time it’s burning, it wears on the sensor and eventually causes it to build up a coating that creates a sort of insulation on it.

This insulative coating reduces the signal returning to the circuit board and then shuts off the furnace because it thinks there isn’t a flame.

Simply remove the flame sensor, clean it with an emery cloth, and then put it back in.

This is a cost-effective repair, but it is only temporary, and you will need to order a new flame sensor.

If you would like to read an entire article on how the clean a flame sensor, replace the flame and where to purchase new flame sensors, then click here: How to Clean a Furnace Flame Sensor in 5 Easy Steps!

3. Check for a Faulty Hot Surface Ignitor

glowing hot surface ignitor
A glowing hot surface ignitor

The process that a gas furnace goes through before sending warm air throughout your home starts with safely igniting your propane or natural gas.

Once the thermostat sends the signal for heating, the circuit board then sends that signal through a series of limit switches and then to the ignitor.

Once the ignitor receives that signal, it either glows bright orange, clicks, or sparks.

After the ignitor is glowing orange, the heating signal opens up the gas valve, which sends gas to the burner section where the ignitor is placed.

Once the flame gets lit, the safety or limit switches tell the circuit board that everything is okay and that the furnace can continue producing heat.

If the furnace control board doesn’t receive the signal that everything is ok, then it shuts off and tries again three times before getting locked out.

So, if you don’t hear the clicks from a spark ignitor or see the glowing orange, then it’s possible that you need an ignitor replacement.

Related Reading: Breaking Down Furnace Ignitor Replacement Cost

The challenge here is that you really need to determine whether it’s not igniting because the part has failed or is not receiving the signal.

failed hot surface flame ignitor
Failed hot surface flame ignitor

In that case, you’ll want to read this in-depth article on flame ignitors or hire an HVAC technician to troubleshoot your furnace.

If you’re not familiar with the above terms, or maybe you have an older furnace, then you might have a pilot light.

If this is the case, then your current furnace has definitely paid for itself, and you’re due for a new one.

But, if you want to troubleshoot your pilot light, then you’ll need to read our article on how to repair and replace or re-light your pilot light.

Related Reading: My Furnace Pilot Light Won’t Stay Lit. What Now?

4. A Clogged Condensate Drain Line is the Worst!

Condensate Drain Line

One of the most common furnace repairs is related to the condensate drain.

And to be honest, when I get a service call for no heat, it’s more than likely a draining issue.

If the condensation from burning propane or natural gas doesn’t get drained properly, then it will stop your inducer motor from moving enough air through the venting to satisfy the pressure switches, and thus the heating cycle won’t start.

This is such a common furnace problem that our industry made a small CO2 tool to blow out these drains, this tool keeps the actual cost of this furnace repair minimal.

This is another reason to get a furnace tune-up annually by a quality contractor.

They will ensure that your condensate drains properly and that your draft inducer motor works correctly.

They will also check your air filter is clean, there isn’t a gas leak and that your furnace’s heat exchanger is in good condition, among other things.

Related Reading: How to Fix a Clogged Furnace Condensate Drain Line

5. The All-Powerful Gas Valve (GV)

single stage gas valve
Single stage gas valve

I’ll start this section off by saying just call a licensed HVAC technician to fix or replace your GV.

With that said, with the right tools, you can at least diagnose whether the gas valve has failed or not.

You’ll need a multi-meter to test whether or not the GV is receiving the signal to open.

You could have multiple issues with your GV; a complete failure, too much gas, or insufficient gas.

One major thing to remember is that if your gas line pressure is off, then it could be causing premature failure of your heat exchanger.

If the heat exchanger rusts out and ends up with holes, then you could have a serious issue with carbon monoxide.

And the furnace repair cost will skyrocket if you need to replace your heat exchanger.

If your GV gets the signal to open, you’ll need a manometer to test the incoming and outgoing gas pressure.

Once you know that information, then you’ll either need to replace the GV, adjust the gas pressure, or call the gas company to pay your gas bill.

A manometer reading the correct gas pressure of 3.5 inches water column
A manometer reading the correct gas pressure of 3.5 inches water column.

Related Reading: The Best HVAC Tools Every HVAC Contractor Should Have

If you want a more in-depth article on troubleshooting and replacing GVs, then click here: How to Diagnose and Replace a Furnace Gas Valve

6. Check Out All The Vents & Ducts

cleaning a HVAC vent

This one is a simple one for your DIY furnace repair.

Walk through your home and check all of your vents for anything blocking them.

It could be as easy as moving a curtain or a piece of furniture that’s obstructing one or more of your vents. This prevents proper airflow.

Checking for air duct leaks can be a bit tougher.

If you want to learn more about finding and fixing air duct leaks, check out this article: Leaking Air Ducts Will Cost You Money! Here’s How To Fix It!

7. Furnace Won’t Turn On?

Furnace access panel safety switch
Furnace access panel safety switch

So now you have checked the basics, and you have gotten as far as firing up your furnace, but nothing happens…

We have a whole article on this if you want to read more about it, but most of it is covered in this guide, so here is the short version.

One of the first things to check is the safety switch on the furnace door.

The furnace door safety switch stops the furnace burners and the fan from switching on while the furnace access panel has been removed.

This is a safety precaution to prevent people from inadvertently burning themselves.

Sounds obvious, but we know it happens a lot.

Check that the access door is secured correctly.

The furnace safety switch pops out when the door is removed.

If the furnace still doesn’t turn on, you will need to check the safety switch.

To check it, open the door, depress the safety switch a few times, and reinstall it.

If you follow all those steps and nothing happens, you may need to replace the safety switch. 

8. Why is my Thermostat Not Working?

Smart thermostat

Another common furnace repair problem that we get called out for a lot is a malfunctioning thermostat.

So when you notice furnace problems with the temperature in your home, or if you don’t hear your furnace kick on when it’s cold, check out the thermostat.

First, ensure you’ve set your thermostat to HEAT rather than COOL. It makes sense, right?

Next, ensure you haven’t set the fan to ON instead of AUTO.

Also, look at the set-point—if you’ve set the thermostat at 68 degrees and it’s 75 degrees in the house, the furnace won’t fire.

Next, replace the batteries. Yes, thermostat batteries wear out; when they do, you won’t see anything on your unit’s LED display.

So even if you can see a reading, go ahead and swap out the old batteries.

Some thermostats don’t use batteries. If that is the case with yours, check the circuit or control board.

You’ll need a volt stick to check for power coming into the thermostat unit.

Consider calling a furnace technician if you’ve exhausted the things here or don’t own a volt stick.

If you don’t already have a programmable thermostat, consider upgrading.

9. Furnace Not Blowing Air Through the Vents?

HVAC blower motor replacement

Whether you have a gas furnace or an electric furnace, they will both have a blower motor.

And I’ll say that if your blower motor has failed, your furnace repair costs will be huge.

There are two main types of blower motors that you might have, a multi-speed motor and a variable-speed motor.

The multi-speed motor is easy to troubleshoot; if it’s getting power (120 volts AC) on the circuit board’s heat tap, it should be running.

If it is getting power and the blower fan isn’t spinning, then you need a new one.

The variable-speed motor is a little tougher to troubleshoot because of the complexity of circuit boards.

The easiest way is to use a tool like the Supco Universal ECM Tester.

Simply follow the instructions in the box and replace the motor as needed.

Sometimes though, people can misdiagnose the blower motor.

It’s possible that there’s not a lot of air movement because of plugged AC coils, dirty filters, or the blower wheel vanes are dirty.

An in-depth furnace cleaning by an HVAC technician can get your furnace running and your home having heated air again.

One last point related to an electric furnace is the amount of air the blower motor moves, designed to ensure that the electric heater elements don’t burn out.

So, if you have an electric furnace, then it’s very important to perform regular furnace cleaning to ensure proper airflow.

Fixing or replacing either of these requires the skill set of a furnace expert. 

Related Reading: Why Is My Furnace Blowing Cold Air?

10. The Bad Furnace Burner

furnace burners

Think of the burner in your furnace the same way you think of the burner on your gas grill.

Like your grill, the fuel for your furnace goes through the burners.

It starts with the gas valve opening, and the igniter and flame sensor work to control the flame.

The flame sensor’s primary job is to shut off the gas if a flame isn’t detected.

Check for a flame first; if you don’t see one, take a second and ensure your gas is on.

But do it—sometimes people forget to pay the bill, or there’s a problem at the gas company’s end.

Look at the color if you know you have access to gas and can see the burner flames.

The burner is clean if it’s a beautiful blue, and the flame is even. A yellow flame usually indicates dirty burners.

Cleaning the burners is a great DIY home project. First, turn off the gas and the power to the furnace.

Then clean the burners with a vacuum cleaner. While you have the vacuum out, clean around the blower too.

Since dust, soot, and condensation can all wreak havoc on your burner assembly, it’s essential to clean it at least once a year.

If the burner assembly isn’t in good condition, replace it. Your HVAC company can take care of that for you.

For info on how to clean your furnace burners, check out: What is a Furnace Burner, and Why You Should Keep Them Clean!

11. The Heat Exchanger

furnace heat exchanger

This is where the magic happens.

Everything from controls to the ignition system works, and the flame shoots down the burner.

Most homeowners won’t ever see the heat exchanger, but that’s why it’s so important to have a professional check it annually by performing a combustion analysis.

This isn’t something anyone can do because the tool to do it properly is expensive.

And it’s expensive because it can save lives.

A combustion analyzer reading safe levels of carbon monoxide

If the combustion analysis comes back and says that the carbon monoxide level is too high, then you most definitely have holes in your heat exchanger, and you’ll be required to stop using your furnace immediately, as it now poses a safety risk.

🛑 STOP: You can read more about the dangers of carbon monoxide leaks here.

If your heat exchanger needs to be replaced, you’re most likely better off asking for a price for a new furnace.

Related Reading: What is a Furnace Heat Exchanger? How It Works and Common Problems

12. When the Noisy Furnace Talks

woman annoyed by loud noises coming from her furnace

You won’t notice much noise coming from your furnace most of the time.

Then, of course, you hear it kick on and cycle off, but if your furnace starts making strange sounds, it’s time to investigate.

Listen for these common S.O.S sounds your furnace makes when it needs help:

  • Whistling
  • Rattling
  • Banging
  • Popping
  • Squealing
  • Scraping

Your furnace may have a loose screw, dirty burners, or a faulty part.

Some noises aren’t from the furnace.

Leaks and other issues in your ductwork can cause noises as well.

Call your service tech when unsure what’s causing the noise. It’s that simple!

Related Reading: Why is My Furnace So Loud?

13. My Furnace Blower Won’t Turn Off!

HVAC blower motor

A furnace blower should only run when the furnace operates.

If your furnace is working correctly, it cycles on and off.

If your blower runs continuously, refer to this post’s thermostat section.

If the thermostat is set to ON, or your set-point isn’t correct, the blower may keep blowing.

Turn the thermostat to AUTO and lower the thermostat temperature.

If this doesn’t trigger your furnace to turn off, keep reading.

Your furnace has a limit switch, and the limit switch can have a manual option.

The manual option overrides your fan control.

If your limit switch is set, the blower will run continuously.

However, sometimes the wires inside the limit switch short out.

It’s also possible you have shorted out wires in your thermostat. 

Both can cause a blower to keep running.

If you have a solid working knowledge of your furnace system, you can troubleshoot and repair it yourself.

If not, call a trusted furnace repair technician to check things out for you.

Related Reading: My Furnace Won’t Turn Off, What Now?

14. Smell a Furnace Gas Leak?

Furnace smells

If you smell a gas leak and the odor is strong in your home, it’s time for immediate action.

Gas, by nature, is odorless; utility providers add the aroma to alert people of a dangerous leak.

So if you smell gas, there’s a problem.

If it’s a gas smell, do not take it lightly. 

If you smell sulfur in your home, natural gas is most likely the culprit, and immediate inspection of its source is required.

🛑 NOTE: You should immediately turn off your gas supply, evacuate your home, and call the fire department.

If you have other weird smells emanating from your HVAC system, check out our article on air conditioning smells for the likely causes. 

Related Reading: Suspect a Furnace Gas Leak Here’s What To Do!

15. Time for a Furnace Room Clean-Up?

messy garage

Sometimes, homeowners don’t feel the need to clean up their basement or garage, leading to a cluttered space.

Not only does it impact functionality in that area of your home, but an unkempt furnace also looks terrible!

Store flammable substances or materials away from your furnace. 

This will avoid unexpected fires, significant damage to your home and danger to you and other family members.

Chemicals such as paints can release volatile organic compounds (VOC) and make their way into your heating system.  

Instead of storing items on or near your furnace, consider the chance you may forget any things.

Then, give your furnace room to operate safely by not doing this.

To maintain the best air quality in your home, you should regularly vacuum and clean around your furnace.

Besides removing any items that could potentially catch on fire, dust can also build up over time inside a furnace.

In addition, a clogged filter will require frequent replacement because it cannot properly circulate air oxygen through the house efficiently.

Related Reading: Everything You Need To Know About Your Furnace Room

16. How Old is My Furnace?

old furnace in a residential basement

Does your furnace look like it comes out of the stone age? 

Furnaces are designed to last approximately 10 to 15 years on average with regular use.

After that, you can expect it will break down more often.

If your unit has reached or passed the warranty period from the manufacturer, you may find that your unit is not running as efficiently as it used to.

This means more furnace repairs and higher utility bills through lower energy efficiency.

This is when you should consider a new replacement furnace

Need Help with Furnace Repair? Call Phyxter Home Services!

Phyxter Approved Logo on Service Truck

We’ve shared a few common furnace repair problems and some solutions.

However, gas furnace repair is complex, and sometimes you need the expertise of a professional heating and cooling company.

Most homeowners can still do many things to keep natural gas furnaces in tip-top shape.

However, the best way to keep your furnace repair cost down is to have a licensed HVAC technician perform an annual furnace inspection.

Regular maintenance can improve system performance and increase energy efficiency.

Regular furnace tune-ups can prevent breakdowns and simultaneously increase your furnace’s service life.

Furnace parts and other HVAC replacement parts can usually be found online; just be sure they are matched correctly to your furnace before installing them yourself.

The safest way to change furnace parts is by hiring a licensed and insured HVAC contractor.

Regular furnace tune-ups can prevent breakdowns and simultaneously increase your furnace’s service life.

You can check out our next article in the series: Furnace Maintenance: Top 10 Tips in 2022 to Keep You Warm This Winter.

Contact Phyxter Home Services when you need HVAC professionals to restore your home’s furnace.

Want to learn more about your home’s heating system? Feel free to check out our other furnace articles!

Jake Gibson

CEO @ Phyxter and HVAC Guru

About our blog

Phyxter (pronounced Fix-ter) is a national home services brand specializing in Residential HVAC, Electrical and Plumbing solutions.

Phyxter is laser-focused on writing the best articles and guides to empower homeowners to get the best out of their homes.

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