10 Common Furnace Problems and How to Fix Them


It can be pretty annoying when your furnace suddenly quits on you late in the night and way past the working hours of your HVAC technician. Having prior knowledge of the common furnace problems and how to fix them may work to your advantage one of these winter evenings.

Knowing how to fix the common furnace problems won’t only help you save money, it also enables you to keep your HVAC system running efficiently. You can’t just sit there in the cold, arms folded, waiting for the day to break. You have to troubleshoot the unit yourself.

Fortunately, several common furnace problems are issues you can resolve quite easily. So, regardless of the situation, you can fix your furnace yourself if you have a little time on your hands.

It’s always better to let professional furnace repair service providers handle the job. But in an emergency, you have to fix the device yourself. That said, let’s explore ten common furnace problems and the appropriate furnace repair tips for them.

#1 Furnace Not Coming On

Issues involving refusal or inability of furnaces to power on are common problems in HVAC systems. You may simply discover your furnace is not coming on one morning.

Unfortunately, situations like this often happen unexpectedly, which leaves you wondering what could be wrong. Before you rush to call the technician, try the following quick fixes.

  • First off, check to see if your furnace is on. It’s also possible that you left the furnace on, but someone else turned it off. So, before you panic, confirm the furnace is on.
  • Next, check to ensure your furnace’s connection to the power source is optimum. We hate to be the HVAC equivalent of an IT help desk, but, at least, we need to be sure your furnace is plugged on.
  • Lastly, check for any breakages in the power cord. A broken power cable won’t supply sufficient power to the furnace, and the HVAC system will not come on as a result.

Most modern HVAC systems have built-in controls that operate the furnace automatically without external interference. Manufacturers design such HVAC units to power on and generate heat without manual influence. You can also apply the fixes above when the furnace is supposed to come on automatically but doesn’t.

The thermostat controls automatic HVAC systems. It sends the signals which determine when the units start or stop. Therefore, the thermostat is usually the first suspect whenever these systems fail to function correctly.

As such, you may want to check the thermostat and ensure it’s working properly in such a situation. We’ll get to how to fix faulty thermostats later on.

Related Article: How Often To Change Furnace Filter

#2 Furnace Not Receiving Power

So, the furnace is connected to a power source, the cable is good, and the system is on. But it’s still not powering up! Now, that’s quite serious, or maybe not.

At this point, you may have to break out some DIY tools and get to actual troubleshooting. But before you start removing screws, do one last check on the power button and cable just to be sure they’re good. Also, don’t forget to check the circuit breaker controlling the furnace.

If nothing changes after checking and running some minor fixes, you can now look inside the system. However, we strongly recommend leaving this part for furnace repair technicians to handle. Attempting a DIY repair may void the warranty on the product, and you may also do more damage to the system.

All you need to do is ensure you connect the system to a power source and put it on. Also, check the electrical panel and reset the breaker. If nothing changes after all these, call the professionals.

#3 Furnace Not Producing Heat

A furnace’s primary purpose is to produce and distribute warm air through the house. And, it becomes a significant problem when the furnace can’t fulfill its primary assignment. The primary suspect when your furnace isn’t getting hot is the thermostat.

You want to ensure the thermostat is on and is set to produce heat. Also, check and adjust the temperature level on the thermostat if it’s low. It should be nothing less than 5 degrees above the room temperature.

In other cases, an issue with the blower fan may make it seem like the furnace isn’t producing heat. In reality, the furnace is producing heat, but the blower fan isn’t circulating it through the room.

To fix the problem with the blower fan, try replacing or tightening its belt. You may also check the owner’s manual’s instructions for other possible solutions.

If none of these solutions rectifies the error, contact the technicians to diagnose the problem and recommend a solution for you.

#4 Thermostat Not Working

Most common furnace problems involve the thermostat. If you think the thermostat is malfunctioning, you should first check if it’s connected and set to heat. If you’re sure the thermostat settings are correct, you can try the following solutions.

Check the thermostat’s batteries. If your HVAC thermostat’s unit runs on batteries, the problem may be flat batteries. Try changing the batteries and see if it resolves the issue. Most technicians recommend that you change the thermostat’s batteries at least once a year.

Also, try blowing out dust and debris from the thermostat compartment. We tend to underestimate the effects dust can have on machine components.

Most furnace repair guides recommend eliminating dirt as a preliminary step to fixing problems with machine components. And lastly, check the breaker in the furnace. If on, turn it off

#5 Furnace Too Hot or Not Hot Enough

Another common furnace problem is inconsistent temperature settings. Again, this issue is often a result of an issue with the thermostat.

The thermostat regulates your furnace’s temperature levels. Its primary duty is to ensure the furnace generates just the right amount of heat. Therefore, inspect the thermostat if your furnace is producing too much or too little heat.

Start by checking whether the thermostat is close to a heat source. Installing the thermostat too close to a heat source may cause false readings. In turn, it’ll regulate the furnace to produce less heat levels. So, you want to ensure the thermostat is recording the correct temperature reading.

You should consider changing to a digital thermostat if your system has the old traditional types of thermostats. A digital thermostat won’t only solve the problem; it’ll also save you money on heating and cooling costs every month. Plus, they’re easier to operate.

Lastly, check and ensure the date and time on your electronic thermostat are correct. This can also affect the furnace’s functionality, especially if you have a set timer on the unit.

If the above solution doesn’t work, the problem may be beyond what you can fix with a DIY attempt. It may be time to call in the professionals.

#6 Furnace Keeps Going On and Off

A working furnace cycles on and off to maintain a consistent temperature in the room. So, if the set temperature on the thermostat is 32 degrees, the thermostat keeps the furnace on till the temperature slightly exceeds that point. Then it cycles off, allowing the temperature to regulate to the desired 32 degrees.

The on and off cycle is essential to ensure the room temperature doesn’t exceed the desired level. Ideally, a furnace will cycle on and off a few times in an hour.

However, when the number of cycles per hour increases, it affects the unit’s efficiency. A faster on and off-cycle will prevent the furnace from heating up to the desired temperature.

You can do a couple of things to rectify this common problem in your furnace. First, you want to ensure there’s sufficient airflow to your furnace. Inadequate airflow to the furnace can cause the unit to overheat, resulting in shorter cycles. To ensure adequate airflow, clean out or replace clogged filters. This recommendation leads us to the next point;

#7 Dirty Filters

Dirty Filters

We cannot overstate the importance of regularly cleaning or replacing the filters in your furnace. Clogged filters restrict airflow in and out of the furnace. This restriction complicates things for the HVAC system. When there’s something preventing air from flowing in, it causes the unit to overheat and increase the furnace’s on and off cycles per hour.

A furnace heats the room by blowing out warm air. But with dirty filters blocking the exit of the warm air from the furnace, it’ll take longer for the room to heat up.

Therefore, clogged filters make your furnace work harder. Working harder will, in turn, cause your furnace to overheat and shut down faster. The obvious fix to this problem is cleaning out or replacing furnace filters as often as possible.

Doing so will ensure you always have unrestricted airflow in and out of the unit. In addition, it’ll keep your HVAC system functioning at maximum capacity without consuming more energy than required.

#8 Pilot and Ignition Problems

Another one of the common problems with furnaces is ignition failure. The pilot and ignition system are especially important to gas furnaces. If your HVAC system refuses to power on, it may be because of an issue with the pilot light.

Several things can be wrong with the ignition system. For example, the thermocouple may be faulty. Or, there may be soot and debris build-up clogging the pilot compartment.

You may also have the flame setting too low, or the safety switch may be defective. However, dirt build-up on the ignition system is still the most common cause of ignition system failure.

So, whenever you notice the absence of a pilot light or one that’s burning yellow, it’s a sign you need to clean the ignition system. Follow the steps below to clean the system.

  • Turn off the power supply to the furnace by disconnecting it from the power source or flipping the circuit breaker switch. Don’t just turn off the thermostat; ensure there’s no power supply to the unit at all.
  • Cut off the gas supply by closing the gas supply valve
  • Using an appropriate tool (preferably a ¼’ hex-head screwdriver), gently remove the flame sensor
  • Clean the sensor by gently rubbing it with fine-grit sandpaper.
  • Wipe up the other parts of the ignition system using a towel
  • Unclog the pilot flame orifice. You can simply blow out the soot build-up or gently use a flat screwdriver to peel off stubborn debris. However, take extreme care to avoid damaging the pilot orifice.
  • Wipe away remaining dust, replace the sensor and reassemble the system.

You need to take extreme precautions as you attempt to reignite the pilot light. Natural gas may build up around the unit when the pilot light goes dormant. Before relighting the pilot, turn off the gas supply and wait for a couple of minutes.

Natural gas is highly flammable and can explode. As such, you need to be very careful. Check the owner’s manual to see the instruction on how to go about reigniting the pilot flame

#8 Furnace Making Strange Noises

Strange squeaking sounds may not require emergency troubleshooting measures since it doesn’t prevent your furnace from doing its job. However, it may be annoying and embarrassing, especially when visitors are in your home.

That said, the strange noises may be coming from a worn-out blower belt. Or, it may be the sound of gas igniting in the combustion chamber. For a problem with the blower belt, you can either try tightening it or replacing it.

For sound coming from the combustion chamber, the solution is to remove excess dirt from the burners. Cleaning the chamber prevents delays in the combustion process and allows the gas to burn smoothly without any noise.

However, if the blower is producing a scraping or grinding noise, don’t ignore it. The noise indicates that the ball bearings in the unit may have worn out, and the blower wheel is hitting against the case. Turn off the unit immediately and call for a professional to help.

#9 Cracked Heat Exchangers

Cracks on the heat exchanger are a common problem that affects the furnace’s overall efficiency. Not only that, but it can also let dangerous carbon monoxide seep into the room.

It’s difficult to tell when there’s a crack on the heat exchangers. However, you should always look for these pointers.

  • Soot build-up inside the furnace
  • Unpleasant smells
  • Water pool on the floor around the furnace
  • House inhabitants experiencing side effects of exposure to carbon monoxides such as headache, nausea, and flu-like symptoms.

When you notice the problem may be a crack on the heat exchanger, put off the furnace and call the professionals for help. You can’t fix the crack yourself, and if you attempt it, you may end up causing more damage. So, let the professionals handle this one too.

#10 Continuously Running Blower Motor

A faulty limit switch may cause the blower motor in your furnace to keep working without cycling off. The lack of an operational cycle will cause your furnace to consume more energy and significantly reduce its lifespan.

First, set your thermostat below room temperature and put the fan on Auto. Under normal circumstances, this should cause the fan to go off. However, if the fan continues to run, check the limit switch and set it to Auto. Don’t trigger manual override, as this setting will cause it to keep running.

If the blower motor doesn’t stop after trying those two solutions, you’ll need to fix the limit switch or the thermostat wiring. Unfortunately, you can’t implement any of those two solutions yourself. Instead, you’ll need to call in a professional to address both issues for you.

Related Article: How to Install a New Gas Line

In the end

The point of this blog post is to enable you to identify some of the common furnace problems and how to fix them. Of course, it’s good practice to contact professionals when you need help, but sometimes, you may have to do it yourself.

Nonetheless, you can avoid most (if not all) of the common problems mentioned above by checking and doing regular maintenance for the HVAC system.

That said, we strongly advise against taking the DIY route to fix your furnace if you don’t have adequate knowledge and skill to solve the problem. You may complicate the issue, making it more challenging for the technicians when you eventually call them.

Here at ALP Heating, we offer speedy same-day services for homeowners who don’t know how to repair a furnace. Call us today to get your furnace working smoothly again.

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