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Twelve Furnace Repair Issues and How to Fix them

You wouldn’t want to find yourself waking up cold at midnight. It’s one thing if you simply need to pull up the covers or throw an extra blanket on the bed. But it’s an entirely different problem if your furnace is malfunctioning or not functioning at all.

Do you have some DIY-experience? Then you might not need any help to diagnose and repair your furnace. However, it would count wise to use a maintenance checklist for your particular heating system, so you don’t miss anything.

Top 12 Furnace Problems and Ways to Resolve Them

Regardless, if you own a high-efficiency gas furnace or just a traditional gas furnace, understanding how your heating furnace system works is essential. You should know the appliance’s fundamental sequence of operation, so you understand what things to look for when there’s something wrong.

Below is a detailed look at a traditional furnace and useful tips to fix its more common issues. If any of these DIY steps makes you feel somewhat uncomfortable, you should, of course, call for professional furnace repair. Saving a few dollars is not worth the uncertainty or an undesirable occurrence involving the furnace.

1.      Confirm that Your Thermostat is ON

Although it might sound silly, you need to confirm that your thermostat is set on “heat” and is at least 1-degree Celsius above your particular room temperature. Quite frankly, a lot of people make service calls even without confirming this!

Below are a few things you ought to check on your thermostat:

Step 1: Check the thermostat’s battery. You might need to replace the batteries on the thermostat. In case your home’s thermostat unit works on batteries, ensure that you are replacing them at least once a year.

Although thermostats are often wired to the furnace low voltage system, some use batteries. So, how is your thermostat powered? Those that need batteries will sometimes flash a low-battery symbol if they need a change.

Step 2: Open your thermostat and slowly blow any debris or dirt that might have clogged it.

Step 3: Ensure that the time and date are precisely set on programmable or electronic models – the system might be on a timer or schedule.

Step 4: Inspect the breaker. Make sure that you turn the breaker OFF before inspecting the fuse for the furnace.

2.      Furnace Isn’t Generating Heat – Reset the Home Circuit Breaker

Generally speaking, there are numerous minor reasons why this might occur. For starters, check that your thermostat is set to “Heat.” Next, try moving up (or down) the dial a few degrees to find out whether you feel a noticeable difference.

In case there is no outcome, check to see whether a fuse or circuit breaker was blown or tripped.

How to Test Home Circuit Breakers:

In your home’s breaker panel, you can find a circuit that controls the entire furnace. The goal is to see if it’s thrown to the “OFF” position, or if it’s in the center.

–  Manually test your breaker by flipping it back and forth.

–  Ensure that it remains in the “ON” position.

That should reset the breaker. In case this doesn’t work the magic, then you either have a problem with the circuit breaker itself or the wiring in the circuit.

3.      Furnace Isn’t Generating Sufficient Heat – Check & Replace Your Clogged Filter

As aforementioned, it is one thing to have a furnace that strains to generate heat and a whole different issue to have one that has somehow stopped functioning.

Do you have a poor-performing furnace that never heats the house sufficiently? The first thing you ought to do is to confirm that the air filter is new, or at least neat and in good condition.

Check & Replace Your Clogged Filter

It’s a much straightforward but integral part of furnace maintenance. A clogged filter is one of the prevalent causes to have a malfunctioning furnace. What’s more, it is the simplest maintenance chore.

Changing your furnace filter frequently is a quick and easy task, and plays a significant role in improving your home’s inside air quality and protecting HVAC components.

– Locate your filter. Most furnaces contain their filter in the intake. Typically, this usually looks like a grate in a wall, ceiling, or floor. Other filters reside in the actual furnace.

– Check the filter. As a general rule, you may know whether the time has come to replace it by holding it up to a light source. In case no light shines through, then the filter requires to be replaced. A dusty, strange smell from the vents, once the blower is on, is another clear indication that you should replace your furnace filter.

– Change your filter. Ensure that you turn off the furnace. No air should also be coming out. Look at the direction your filter is pointing. Typically, filters are designed to trap materials blown from a certain direction. Setting up your filter upside-down might lower its effectiveness.

Besides, cleaning the dirt that accumulates on your filters will help with the flow of air. So, what happens with a clogged air filter? It means that the air handler needs to work more to make up for the blockage of airflow. Apart from increasing your utility bill, the limited airflow through your cooling & heating system might make your heat exchanger overheat and even shut off too fast.

Filters usually clean the air passing into the furnace, as well as the heated air that’s sent back into the home. A dusty, clogged filter blocks the airflow and ultimately causes pressure and heat to build up in the furnace.

Mostly, newer and more efficient furnaces are vulnerable to the issue and will shut down before a dusty filter brings more problems. In other units, furnaces might continue to operate but with reduced efficiency and less heat output.

4.      Safety Switch on the Furnace Door

In case your furnace is not working, the first step you must take is to look at the safety switch on your furnace door. Typically, a furnace door safety switch primarily prevents the burner and fan from coming on during the access panel’s removal.

Furnaces usually have a safety switch that comes out once the door is removed. If you want the switch to be activated and the furnace to work, the door should be in place!

In case you realize that you ought to set up a brand-new safety switch, here is a step by step instructions on how you could set up one for your Furnace Door.

– Turn off the power

– Prepare the blower door

– Wire your safety switch

– Inspect & test the installation

5.      Maintain a Clean and Unobstructed Area Around Your Furnace

Although this might seem like an obvious thing, homeowners with busy lives sometimes forget to attend to some of their home areas, such as the basement.

Once a basement is cluttered, it might result in the area surrounding that furnace being filled with debris and unnecessary items. Apart from having improved performance, a clean surface will also look much better.

Avoid keeping flammable materials or substances near your furnace. Generally, crowding your furnace might result in unexpected fires, substantial damage to your house, and risk to your family members and pets.

It might seem quite convenient to simply “keep it there” during summertime. However, consider the likelihood that you might well forget any possessions you have left on or close to the furnace. As a result, give the furnace the space it requires to work safely.

What’s more, vacuum and clean frequently around the furnace. Although you might have removed all flammable materials from that area, don’t forget that lint and dirt can accumulate and cause a fire hazard. Besides, an excess amount of lint and dust can also make your filter clogged sooner than expected, demanding more regular replacement.

6.      Check the Burner Flames

In most cases, the failures related to burners originate from contamination. Because of this, you’ll have to inspect your burners and ensure that they’re free from debris. You will need to ensure that you have clean burners and the best way to do this is to check the flames.

Are they even and blue?

If so, your burner is probably clean. In case they are yellow, you most likely have dirty burners. Although a vacuum cleaner is useful when it comes to cleaning your burners, just ensure that you turn off the power and gas before everything else. Another region you ought to clean with your vacuum cleaner is the area around the blower.

Undoubtedly, dust might build up in summer. As a result, you must inspect and clean the furnace burners – especially before the beginning of the colder seasons.

A mixture of soot and condensation can cause burners to work ineffectively and might also cause other furnace issues. The prudent thing is to clean the burner assembly yearly or change it the existing one is in bad condition.

7.      Oil the Furnace Blower Annually

When preparing the furnace for winter, it’s essential to ensure that each component is clean and in good condition.

The furnace blower’s primary role is to take the heat from the furnace and then distribute it all over the house. Extend the life of your furnace by keeping the furnace blower lubricated.

Below is a list of 7 simple steps of how to oil your furnace blower motor:

  1.  Switch the circuit breaker off at the main central panel that provides the furnace’s power.
  2.  Use a screwdriver to detach the screws and remove the furnace’s access panel.
  3. Find the blower motor assembly close to the furnace’s base. Remove the bolts attaching the blower motor to the main assembly of the furnace with a wrench.
  4. Find the set screw on the blower motor housing’s side. Detach the bolts. Then, pull the motor from its housing.
  5. Identify the oil parts on the shaft and motor.
  6. Squeeze 2-3 oil drops into each port.
  7. Activate the furnace. The blower motor will run much better with the new oil.

When it comes to how your heating system works, the furnace blower motor has a significant role. It needs to be oiled once every year and it should not make any strange noises when started.

8.      Look at Your Limit Switch

A poor limit switch might cause the blower to run constantly, and because of this, it will significantly reduce the blower’s lifespan.

Hiring a technician to replace the limit switch will quickly fix that issue.

So, how can you test whether your furnace problem is the thermostat or the limit switch?

If it’s because of a bad high limit switch, the furnace shouldn’t fire. In case the high limit switch trips, the heating/ flame element will soon be turned off and the blower will go on clearing the heat. In fact, the blower will operate until either the limit switch closes, or the system is reset.

Usually, limit switches are closed, and they should fail open. That means that when the temperature gets too high, or they go bad, they open the circuit. In case the circuit is open, you will need to change the limit switch.

9.      Look at Your Pilot Control or Electric Ignition

Gas furnace operation can have electronic control or work with a pilot light, which does away with the need for a constant flame.

A malfunctioning ignition system like the ones in furnaces with a thermocouple might drastically lower the furnace’s ability to efficiently heat the house. Clogs or drafts in your heating system might lead to your pilot light shutting off.

Most newly introduced systems ignite electrically, instead of by standing pilot light.

The action steps that you may take are:

  1.  Turn off the furnace power switch and then back on (the ignition might need to be reset).
  2. Turn off gas and power to the furnace to enable inspection of the heating element. Make sure that you don’t touch the heating element. However, if it looks damaged or cracked, you will have to change the igniter.
  3. With the assistance of the furnace’s manual, check out the steps suggested by the manufacturer to troubleshoot the operation. Just like with the pilot light, you could actually destroy the system and your house if you ignore the steps or safety methods during this task.
  4. Follow the instructions and in case it doesn’t work, contact for service.

10.  Heating or Rapid Cycling Issues

Many causes exist when it comes to a furnace turning on and off too fast. Of course, the first cause might be a worn-out or dirty air filter. In case you haven’t changed it in recent times, try it out – it is an easy and quick fix.

So, when do you call a professional? In case a new filter doesn’t fix the issue, you might be dealing with a more serious situation. Perhaps, there is a problem with the blower motor and belts. They both demand the service of an expert.

11.  Furnace Doesn’t Blow Air

Check out the furnace’s inspection window. Ensure that the blower is debris-free. What’s more, there has to be a flashing light; red or green.

Always confirm with the manual. If the light shows green, it is alright; if red, reach out for service. In case there’s no light, the furnace problem might be with the transformer, furnace control board, the run capacitor, the blower motor, or the thermostat.

12.  The Gas Furnace Blower Runs Constantly

Typically, the blower is situated between the furnace and the return ductwork. Cool air is usually passed by the blower through the heat exchanger and heated before being passed to the plenum and finally sent all over the house by the supply ducts.

More often than not, a continuously running furnace that never shuts off can indicate a required repair. Make sure/ confirm that your thermostat isn’t set to “continuous fan”.

Next, turn down the temperature to see whether this step fixes the issue.

A gas furnace that doesn’t turn off might also be a sign of an issue with a faulty limit control switch. (This might require resetting or replacing).


Hopefully, this article has taught you ways to resolve some of the common furnace issues. Have you experienced any of the above DIY repairs?

Getting your system inspected routinely, and at least as frequent as the manufacturer recommends, may prevent a minor repair issue from deteriorating. Trying out DIY repairs can be affordable and satisfying. However, it’s essential to ensure that you have the relevant skills before trying out any work on your furnace.

In case the tips don’t help you identify or fix issues or if they’re above your skill-level, you might need the services of a reliable furnace repair professional. It’s essential to maintain routine tune-ups and cleaning of your HVAC system.

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