Common Furnace Repair and Problems [With Pictures How to Fix]

When you wake up on a cold morning, you can barely get out from under the covers. After taking a hot shower, you head downstairs and crank up your thermostat. But after some time, the house isn't getting any warmer or receiving hot air from its vents! You're going to need a furnace repair! When this happens, it feels like nothing could be more frustrating! But don't worry, read on this blog to learn about how your gas furnace works, some do-it-yourself fixes you can try, signs of significant issues that need a professional heating repair, and how to prevent another furnace repair in the future.

And don't forget, if you live in or around our Baltimore service area and need an emergency furnace repair, call SuperTech HVAC! Our HVAC experts genuinely care about providing your family with a safe and comfortable home. 

For any furnace problem, we're the repair service you're dreaming of. So give us a call or schedule here!

On a side note, if you also have a heat pump and suspect it may have a problem, this blog might be helpful. Also, keep in mind that our company works on gas furnaces. If you need an electric furnace repair, one of these great companies may be able to help.

Don't Hesitate; We're The Contractor You Need For A Fast Fix!

How A Gas Furnace Works

Before you can understand your gas furnace's problems, you need to know how it provides heat. This will make it much easier for you to perform a heater repair on your own using at-home fixes. This method could save you a lot of money!

To begin, when your thermostat senses that your house is colder than the desired temperature, it sends a signal to the furnace's control board. This begins a process known as "combustion," in which fuel and oxygen mix and burn to create heat. This starts with your furnace's gas valve opening, ignition flame sparking, and draft fan spinning. Then, the air from your house's rooms gets pulled in through the supply duct and delivered to your furnace.

Once that has happened, the fire inside your furnace warms the air before distributing it back to your rooms through the return duct. Meanwhile, combustion fumes produced from burning gas pass through the heat exchanger and get expelled through the flue pipe.

We understand that that explanation may have sounded a bit confusing. So to help you understand the process more clearly, we've included this step-by-step video as well:

You should also know that if you have a heat pump, it is not part of your furnace's process. These condensers heat your house with your air handler and may assist in the air conditioning process.

Now that you've educated yourself on how a furnace functions let's talk about some easy DIY fixes! Hopefully, these can solve your furnace issue.

Try These DIY Fixes First!

Step One: Set Thermostat Correctly

As we mentioned, the heating process starts with you setting your thermostat to "Heating" mode. After you do this, it transmits a signal to the furnace's control board to begin combustion. So make sure you have your thermostat on heating mode at the correct temperature. No heat will be provided if it is set to "Cool."

Thermostat Heating Mode

If the settings are correct, but you do not feel any hot air, the thermostat's batteries may have died. Change them if so. If that was the only issue, the signal should go through, and the heating process should start again.

For more information, check out our blog on why your thermostat isn’t working.


Step Two: Turn Furnace Switch On

The furnace switch provides power to the system when it is flipped up in the "On" position. It looks like a light switch and should be on the side of your furnace or nearby on the wall.

Furnace Power Switch

If you have no warm indoor air, check the furnace unit and find the switch. If it is flipped down, it is off and not providing power to the unit. Make sure to flip it back on, and hopefully, your furnace will resume its heating.

Additionally, you may be wondering why the switch got shut off in the first place. Well, since it looks like a light switch, it can easily be mistaken for one. Someone likely flipped it off because they thought they were turning off a light.

Step Three: Turn Your Tripped Circuit Breaker Back On

Your furnace is connected to your house's breaker box so that it can receive electricity. So if an electrical surge or power outage trips the furnace breaker, you will need to reset it.

In this case, check your house's breaker panel and spot the furnace's breaker. If it is flipped in the "Off" position, your furnace will not receive power. Switch the tab to "On" to get the electricity running again.

Furnace Circuit Breaker

Step Four: Open Gas Valve

The gas valve allows gas to flow into the furnace, which is essential for heating. Some units feature an exterior gas valve that you can manually open and close. If it has been shut off, open it back up so that the furnace's fuel source can return.

Damaged Gas Valve

Also, if your furnace receives its gas from a propane tank, that fuel will eventually run out. So if you are not getting any warm air, check to see if your propane tank is empty.

Step Five: Clean Your Dirty Air Filters

Inside your furnace, filters ensure that the air you breathe is safe and clean. Over time, dust and other unsafe material can accumulate within your ductwork. Filters trap that material and keep it from blowing into your house.

However, over several months, HVAC filters can become so clogged that air cannot pass through them. Therefore, check your filters if it has been three or more months since you changed them. They need to be changed if they have become very dark-colored or covered in visible dirty and fuzzy material.

Changing Furnace Filters

We at SuperTech highly recommend changing your filters monthly for better system efficiency. Also, be aware that filters can be located in several different places. If you’d like to learn more, we have an entire blog that discusses the importance of changing your furnace filters.

Step Six: Open And Unblock Air Vents & Registers

Your house's vents and registers allow air to get pulled into and released out of your air ducts. The return vents take air in and distribute it to the furnace, while the supply vents pass it back to your rooms.

House Supply Vent

On that note, many homeowners think that closing vents in certain rooms helps lower their energy bills. However, this can lead to several problems, such as duct leaks and higher energy usage in homes with ECM blowers. So if you are in a chilly room, look to see if its air vents are closed.

You should also check if your vents have been covered by furniture such as tables, couches, or bookshelves. This can also block air from getting into your house. If so, move those items out of the way.

Step Seven: Relight The Pilot

Not all furnaces have pilot lights, as they mainly exist for older models. But for those that do, they keep the flame inside your heater running. If your system has a pilot, it is probably at the bottom of your furnace, toward the front of the access panel. After the valve opens, the pilot's flame ignites so the gas can heat up your house's air.

Damaged Furnace Pilot Light

Speaking to that, if your furnace's pilot light gets blown out, this will prevent the gas from getting heated up. Fortunately, you can relight your pilot on your own! Want to learn how? Check out the furnace section of our blog on pilot lights going out.

What's more, another system in your house that may have a pilot light is your water heater. To learn about issues that it may have with lighting, you can read this section of our pilot lights blog as well.

Signs You Need A Professional Furnace Repair 

If your furnace still isn't working after trying all of those fixes, you have done everything you can and need to schedule an expert furnace repair.

That being said, if you are planning on calling a furnace repair service it helps to be aware of the problems your furnace may have and what caused them. That way, when an HVAC technician performs a gas furnace repair, it'll be easier to understand what they tell you.

Let SuperTech Restore The Heat You're Looking For

Thermostat Is Faulty

Thermostats can face numerous technical issues that prevent their heating signal from getting transmitted. Without that signal, your furnace's heating process cannot start. 

Elaborating on that, you can easily tell that your thermostat has an issue if it becomes unresponsive or its screen display goes blank. Furthermore, many newer models will alert you if they have a problem, either by naming an error on their display or showing the word "Error" (or just "E").

Thermostat Error

Something else you can do is look on the inside of your thermostat to see if its control board and wiring are covered in dust and dirt. This can interrupt the transmission of signals, creating a furnace emergency at the start of the process. However, don't try to do anything with these electrical components if you don't know how to handle them.

Other causes of a faulty thermostat include a bad control board, poor wiring, incorrect programming, a damaged high-voltage wire blocking transmission, or the unit becoming old.

Circuit Board Not Working Properly

Your furnace's circuit board will typically be located behind the access panel, inside the blower chamber in front of the fan. After receiving the thermostat's heating signals, the circuit board supplies voltage to the blower motor and burner so they can run. And with the board serving as the furnace's brain, the heating process can shut down if it malfunctions. 

Furnace Control Board Issue

One indicator of a circuit board issue is not hearing your blower fan spinning inside your furnace. This may be because the board has prevented the fan from receiving the proper electricity it needs. You may also feel cold air blowing out of your vents because the control board has failed to turn on the burner. Something else to look out for is water leaking from the furnace: a leak can drip water onto the control board, causing damage or corrosion to the electrical components. If this happens, it may be unrepairable.

Loose Or Faulty Draft Inducer Motor

The draft inducer motor is located near the heat exchanger inside your furnace, toward the top. After the thermostat sends its signal to the control board, the draft inducer motor pulls fresh air into the furnace's burner so that any remaining gas fumes from the furnace's last heating cycle get removed. This helps make for a more efficient gas-burning process that keeps the air in your house safe to breathe. It also helps keep your furnace's burners clean by preventing the development of soot.

Furnace Draft Inducer Motor

That being said, a faulty inducer motor can cause your furnace to run less efficiently, and it may flat-out not turn on if the motor breaks. If your house is not getting any hot air, go to your furnace's indoor unit and listen for tapping, humming, rattling, and/or knocking sounds. Those are all possible indicators that the inducer motor is loose. You can also try shutting off the power to your heater and removing its access panel to feel for heat. If the inducer motor is too hot to touch, that is another sign that it may have failed.

Hot Surface Ignitor Is Cracked Or Broken

The hot surface ignitor is also inside your furnace and usually attached to a bracket shaped like a "V." It is responsible for getting the heating started after gas starts flowing into the system. The hot surface ignitor receives electricity from the control board, sparks a flame, and glows red with heat so that when the gas reaches the burners, it can instantly warm up.

Damaged Hot Surface Ignitor

When searching for the cause of your house not receiving hot air, pull off your furnace's door panel. If your system is turned on and you do not see a flame under the hot surface ignitor or the piece glowing red, it is not working. Your hot surface ignitor may also break if it cracks or the control board does not supply enough voltage for it to get hot.

Interior Gas Valve Is Closed

While some furnace models have a gas valve on the outside, they all have one on the inside. Once the surface ignitor gets hot enough, the gas valve opens to allow fuel to flow into the heating system.

Problematically, if the gas valve is closed and the system is not receiving gas, your furnace will have no fuel to burn and produce heat. You will then, of course, feel no heat coming out of your vents. Possible causes of your gas valve not working include age-related wear and tear, the piece getting submerged in water due to a leak, issues with electrical components (such as the gas ignition system or a shorted safety circuit), and a faulty flame sensor misreading the interior temperature of your furnace and cutting off the gas flow.

Flame Sensor Cannot Detect Fire

The flame sensor is a safety device for your furnace. A thin metal rod, it is located toward the bottom of your furnace's interior burner assembly in front of the pilot light. The flame sensor detects if the fire inside your furnace is burning to allow the gas valve to open. If it has not sensed a flame in about seven seconds, it will automatically shut off the gas flow.

Damaged Flame Sensor

Due to its proximity to the pilot light, the flame sensor can get coated in material such as dust over time and become too insulated to detect a flame. If your furnace is not blowing hot air, a possible cause is that the flame sensor did not sense a flame, keeping the heating process from starting. Another symptom of a faulty flame sensor is short-cycling, meaning your furnace will repeatedly turn on and off due to the flame sensor detecting a flame intermittently.

Broken Blower Motor

The blower motor is also inside your furnace toward the bottom of the unit and part of the blower fan. It pulls air in from your house and blows it back through the vents into your rooms after it gets heated. So if the motor isn't working, the heating of the air will stop dead.

Bad Blower Motor

To make things clear, you should hear the blower fan spinning when your furnace is running. So if you suddenly don't hearing it, this is an obvious indicator that it has stopped working. Also listen for squealing, grinding, scraping, and thumping sounds, as well as short cycling.

Furthermore, the blower can stop spinning if its motor is dirty or fails due to duct blockages. This can make it work harder to try and blow air back into your house to get it to the right temperature.

For a more elaborate guide to your blower fan not working, check out our blog on HVAC fan repairs.

Heat Exchanger Is Cracked

Inside your furnace, the heat exchanger is a set of coils located directly above the blower fan. These coils pull hazardous gas out of the warm air before transferring the air back to your house. It contains the system's hottest flue gas and is located near the burner, so it gets directly warmed by combustion gas and fire.

Furnace Heat Exchanger

The most apparent - and most significant - sign of a heat exchanger issue is if you start feeling unusually dizzy and tired or losing consciousness. It may be occurring because the coils have cracked due to your system leaking water, rust/corrosion, poor air circulation, or wear and tear due to age. This can release the chemicals that the heat exchanger contains, which may create severe consequences for your and your family's health.

Beyond this, if cold air is coming out of your vents while you are experiencing chemical overexposure symptoms, that will make it even more evident that the heat exchanger has cracked. And if you do start to feel those symptoms, make sure to shut down your system, open the windows, and get an HVAC technician to come out and address the crack as quickly as they can!

To learn more about heat exchanger cracks, read our blog about them.

Limit Switch Is Activated Or Damaged

The limit switch is located behind your furnace's cover panel and is responsible for monitoring the temperature of the air as it passes through the heat exchanger. If the temperature is sufficient for the heating process to proceed, the switch will allow the blower motor to turn on. The limit switch will also shut your furnace down if it overheats.

On that note, your furnace not turning on or blowing cold air are possible symptoms of the limit switch being dirty or damaged. Your heater may also begin to blow hot air inconsistently if the limit switch has caused the furnace's safety cycle to get activated at the wrong time.

Activated Or Faulty Flame Rollout Switch

The flame rollout switch is another safety device, usually located inside your furnace on the front of the burner. If your furnace is experiencing an issue such as a cracked heat exchanger, a dirty combustion chamber, or a blocked flue pipe, it can lead to a malfunction in which flames literally "roll out" of the combustion chamber. Because this is a fire hazard, the rollout switch exists to shut your system off and prevent worse damage from occurring.

Rollout Switch

If your furnace won't turn on, it may have experienced flame rollout and shut down. However, it is also important to know that if the rollout switch is faulty, it may deactivate your system mistakenly due to thinking that flames are rolling out of your system when they are not.

Even worse, if your rollout switch deteriorates to the point where it cannot detect flames escaping, your system may experience unrepairable damage. A broken system may mean you need to get a furnace replacement.

Pressure Switch Is On Or Broken

The pressure switch is in place to shut down your HVAC system if it has not adequately expelled all of the flue gas, as a backdraft may otherwise occur. The switch will be located near the draft inducer motor. Like with the rollout switch, your furnace may not be on because the pressure switch was activated to prevent a dangerous situation. 

The pressure switch can also become dirty, worn, or damaged, causing it to malfunction and not shut your system down. So if you are experiencing symptoms of CO poisoning, your furnace's pressure switch may have an issue.

Bad Pressure Switch

Door Switch Not Secure

The door switch is another safety feature behind the furnace's door panel. It prevents your system from carrying out the heating process if the door panel is open or unhinged, as having the system run with its flame exposed is a fire hazard! Check the condition of the furnace's door panel: if it is not securely attached, you may need to have it readjusted so that the door switch can detect that it is closed.

Furnace Door Switch

Clogged Condensate Drain Line

The condensate drain line is also unique to a standard-efficiency furnace. It runs through your wall and connects your indoor unit to the PVC pipe outside your house near the condenser. After condensation gets produced, this drain line is in place to catch the water that drips off the system and transfer it to a pan so that it won't spill onto the floor. 

If you find water on the floor near your furnace, the drain line may have become clogged by excessive dirt and debris. This can cause the drain pan to become weighed down and stress its connection to the drain pan, wearing out the system and possibly loosening or disconnecting it from the pan. In addition, drain line problems can cause the drain pan to become flooded and leak onto the floor.

And, of course, if you have a water safety switch for your system, it will shut your furnace down after detecting a leak, explaining why you are not getting any hot air.

Blocked Drain Line

Metal Flue Is Blocked Or Cracked

A metal flue pipe is only found on an 80% "standard-efficiency" furnace. If you are not sure whether yours has one, you can spot it coming out of the top of your indoor unit. After the heated air passes through the heat exchanger to remove the gas fumes, the fumes are expelled outdoors through the flue so that they do not remain inside and cause harm to your family.

Elaborating on that, if you smell combustion gas or are experiencing side effects of CO poisoning, something in the flue pipe may be blocking the fumes from getting sent outside. Sometimes, this can actually result from birds unknowingly flying into the flue. Any flue blockage can cause the dangerous exhaust gas to escape from the pipe into the house. So once again, turn your furnace off and schedule a repair if you smell chemicals in your home!

Rusty Furnace Pipe

Another possible error with the flue is a "backdraft," in which excessive air gets pulled down through the pipe, stopping the gases from getting expelled and causing them to leak into your home. One sign of a backdraft is white corrosion on the flue, typically near the "elbow," or the part that curves at a ninety-degree angle. Furthermore, flue gas can get blocked from exiting if the flue is undersized or has too many ninety-degree bends. This can lead to pressure rising inside the pipe, which can crack the flue and cause the exhaust gases to leak into your home.

Clogged Or Cracked PVC Exhaust Pipes

PVC exhaust pipes exist only on a 90% "high-efficiency" furnace. Unlike the metal flue, there are two plastic pipes rather than just one. Because high-efficiency furnaces produce condensation, one pipe is responsible for pulling in fresh air from outside. The other serves the same purpose as a metal flue: expelling gas fumes.

80% vs. 90% Furnace

If you see water leaking from your high-efficiency furnace or smell gas in your house, there may be a problem with your PVC pipes. For one, the condensate pipe may continue leaking if your system's water safety switch is faulty and fails to shut the system down. It can also deal with the same blockages as flue pipes due to factors such as birds flying in, too many ninety-degree angles, and backdrafts.

Ductwork Is Leaky Or Restricted

Your ductwork must be completely free of any openings if you want warm air delivered back to your rooms. So if cracks or holes exist in your ducts, hot air can and will escape from places where it shouldn't!

A common sign of your air ducts having holes is certain rooms feeling significantly colder than others, as more air will pass to specific locations than others. This will make those areas significantly hotter since they are receiving more warm air than they should, while others will become colder due to receiving less warm air.

Furthermore, as we mentioned in the blower motor section, obstructions in your ducts can make the blower fan work harder to try and heat your house to the right temperature, causing the motor to work too hard and break. This can make your heating system completely unable to warm up your house. For that reason, getting a seasonal duct cleaning is always a great idea.

To learn more about what may be inside your ducts, visit our blog on the subject.

Sealing Ductwork

How You Prevent Future Furnace Repairs

A gas furnace should last at least ten to fifteen years, but its lifespan can be extended if it receives regular maintenance. And what's even better, tune-ups can help lower your energy bills and make furnace repairs less frequent. Maintenance allows for all your system's components to be checked so any developing issues can be spotted, allowing you to address them early. It is always the most efficient way to prevent a broken furnace.

SuperTech technicians perform super thorough furnace maintenance. They use a checklist to inspect each component of your system individually to see if they are all stable. Once they are finished, they tell homeowners how their systems are working as a whole and whether they have issues to address.

Our technicians can also perform tune-ups for other heating systems, especially your heat pump. We also provide other general heating services. You can clearly see that we offer even more than you could ask for!

Need maintenance for your furnace? A tune-up is how you avoid a pesky furnace repair that could cause you to require another emergency service. Schedule an appointment with us to get the furnace service you are looking for!

Freezing Air Is A Pain; SuperTech Will Drive It Away!

Have Your Furnace Ready To Combat The Heat!

When it's chilly out and you're inside, all you want is to relax and get warm. But that can't happen if an issue with your furnace prevents it from supplying warm air! So every year, it is wise to schedule cooling maintenance for your furnace. That way, a technician can check if it is in an overall stable condition.

And if you are a homeowner in or around Baltimore who needs a furnace repair, SuperTech is your best HVAC contractor! We've been reviewed positively hundreds of times and care about your time. Therefore, our skilled technicians will make sure to show up at your doorstep with a smile, get right to work on performing their furnace repair, and make sure you fully understand their diagnosis and suggestions for how to ensure that you'll maintain warm indoor air quality. 

Also, do you need a new furnace installation? We can give you a free estimate and find the perfect new heating system for your home and budget!

Looking for the best professional repair for a furnace breakdown? Book online or give us a call now for the best HVAC service you could ask for!

SuperTech Repairman Furnace Maintenance

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