Nearly half of the houses in the U.S. rely on gas furnaces for their heating, making it an even more popular option than furnaces powered by electricity. As the winter months roll in and you start relying on your heating system more often, you’ll want to make sure you’re prepared for any issues that may arise.

Knowing the most common problems that might crop up with your gas furnace—as well as their solutions—might just be the key to keeping your home warm this winter. That’s why R & S Mechanical has put together this guide with the 10 most common gas furnace problems.

How A Gas Furnace Works

Knowing how your gas furnace works when it is running smoothly might make it easier to understand what the problem is when it isn’t.

A gas furnace operates by taking in cold air, cleaning it with an air filter, then heating that air up with a gas burner. The warm air is then distributed with a blower motor through ductwork. As the hot air enters the home and eventually cools down, it is collected again and returned to the furnace, and the process begins again.

Gas Furnace Isn't Heating

One of the most obvious signs that something is wrong with your heater? It stops heating. If your furnace stops blowing hot air, or even begins to blow cool air, there are a few things you can check by yourself before calling a professional:

  • Check to make sure the heat registers are open.
  • Check the thermostat.
  • Check the furnace’s power source.

If you go through all of these and everything appears to be in working order, it’s time to call in a heating repair technician.

Strange or Especially Loud Noises

If you hear any out-of-the-ordinary noises from your furnace, it’s best to check these right away. For instance, if you hear humming, squealing, or banging, it might be an indication that it's time to replace the filter or oil the blower motor.

Whether it’s something you can fix yourself, or even a small problem a professional can help with, getting to it earlier is likely to save you a lot of money and stress in the long run.

Frequent Cycling with Your Furnace

One of the most common problems people experience with their furnaces is known as “cycling”. This occurs when your furnace turns on for a short period of time, then off for a short period of time, and repeats these short cycles over and over again.

This can lead to higher-than-average energy bills, and damage to your furnace. If you’re dealing with this “short-cycling”, there are a few things you can check:

  • Make sure the filter isn’t dirty.
  • Check the exhaust vent for a blockage.
  • Double check that the thermostat reading is accurate.

Blower Will Not Turn Off

If you notice that your blower is consistently blowing without turning off, there are two potential culprits for the problem.

It may be that the thermostat is set to its FAN setting, keeping the blower on. This is quick to blow out the motor, and it’s usually best to keep your settings on “Auto”, to make sure it is only on when your HVAC system is working to heat or cool your home.

It may also be that there is a problem with your fan limit switch, which is supposed to monitor the temperature on the inside of the furnace and turn off when the intended temperature is reached.

If the blower is going all the time, it may mean that the fan limit switch is not correctly reading the temperature, and is keeping the blower running. This can often be solved by resetting the fan limit control, but it may also need replacing.

Gas Furnace Pilot Light Is Out

A pilot light is a small flame that is kept lit and serves as an ignition source for your gas appliances.

If it goes out, your furnace will not be able to produce heat. On top of that, the gas valve supplying the fuel might still be pumping gas, which can result in a dangerous buildup of gas. It may even lead to gas leaking into the living space.

There are a few reasons your pilot light might be extinguished: It might be that a strong draft has blown it out, or dirt has built up in the gas tube. It also may be the result of broken or malfunctioning thermocouple, which would cause the gas to shut off.

If it is simply a matter of the pilot light having been blown out, you can usually relight it, as long as there isn’t gas buildup. If you need to replace the thermocouple, a furnace repair technician can help you do this fairly quickly.

The Furnace and Thermostat Do Not Match

When your gas furnace and thermostat are working together correctly, they communicate with each other to keep your house at a comfortable temperature. When they are not matched, your furnace may not get the cue that it is time to kick in or shut off, causing your heating to malfunction.

There are three types of thermostat systems: millivolt, low voltage, and line voltage. To make sure yours is compatible with your furnace, you’ll need to have the correct type. A heating services expert can advise you on which is right for your home.

Thermostat is Broken

Similarly, if your thermostat is broken, it can not accurately communicate to your furnace. You may set it to a certain temperature, but find that your furnace stops heating at a temperature significantly cooler than what your thermostat is reading.

To make sure yours is working properly, make sure it has power, and that there isn’t any dust getting in the way of the inner components. If that doesn’t do the job, a professional can help you determine how to calibrate your thermostat.

Dirty Furnace Filter

The air filter on your system is vital to proper function. If it is clogged, the airflow throughout your house can be compromised, which causes the heat exchanger to get too warm, and then turn off. This can sometimes be the cause of short circuiting, which increases your energy bill and decreases the lifespan of your furnace.

Replacing the filter regularly can help avoid this problem. Scheduling a yearly furnace tune up can help ensure your furnace is running efficiently

Electronic Ignition Is Failing

Some furnaces are not ignited by the old-school standing pilot light, and instead rely on electric components, like a high-voltage electrical spark or an electronically-controlled element, to ignite the burner.

If there is an issue with one of these components, it may prevent your gas furnace from producing hot air.

To remedy this, try replacing the filter and checking the power to your furnace. If those steps don’t work, you may need to call a professional to check out the electronic ignition.

Furnace Clicks but Doesn’t Turn On

In some cases, you’ll hear the same click you always do when switching on your furnace, but the heat won’t start.

There are a few culprits that may be causing this problem:

  • Insufficient power supply: If your gas furnace isn’t getting enough power from the circuit breaker, it won’t turn on.
  • Faulty thermostat settings: Your thermostat may be reading incorrectly, which means your furnace doesn’t know it's time to kick in.
  • Electronic ignition problem: It may be a result of an issue with the flame burning ineffectively.

If it’s a result of an issue with the power supply or thermostat, try resetting it by turning off the circuit breaker for around 20 minutes, and then turning it back on.

This issue may also be caused by a broken fan or other heating elements, in which case it's a good idea to call out a team of experts to take a look.

When to Call a Heating Expert

While there are some common gas furnace problems that can be remedied without the help of a pro, in many cases, you want an experienced furnace repair company to correctly diagnose the problem and fix it quickly. If you’re a homeowner in the Raleigh-Durham area in need of a gas furnace repairs, call us today at (919) 302-8956 to set up an appointment.