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You have an expectation when you start your furnace that it will warm your house. However, occasionally you may notice that it is not blowing hot air. When this happens, it is helpful to know how to troubleshoot the problem. Yes, you may need to call a professional HVAC technician, but there are some things you can check to get the heat blowing again.

Problems With Your Thermostat

Your thermostat is the brain of your HVAC system when it comes to temperature. If there is a problem with it, you won’t get the desired hot air into your home. There are a few things about your thermostat you want to check and confirm.

First, check the batteries in the device. You should plan to change them every six months to ensure they do not fail when you need you need it.

Next, check to make sure the HVAC system is set to heat. It is common to forget to switch from cool to heat when the weather changes. Also, be sure you check the fan is set properly. Set the fan to “Auto,” so it runs when the furnace is cycling.

Finally, check to make sure the temperature is set properly. If you live with others, you may find the temperature has been adjusted by someone else.

Old or Clogged Filters

Your HVAC system works on a simple premise of circulating air through the system and dispersing it into your home. If there is a restriction in that system somewhere, then it cannot do its job properly. The air filter is one of the first places a restriction is going to happen. It has a simple yet very important job to keep dust and dirt out. However, clogged filters will not let your HVAC system work effectively.

Most filters will last between two and three months. However, you should plan to check your filter monthly for dirt and dust. If you can see dust forming on the intake side of the filter, it is time to either clean the filter or replace it. If you don’t change a dirty filter as often as you should, your HVAC system will be put under strain. This could damage other parts of your system.

Faulty High Limit Switch

To keep you safe, your furnace has a host of safety sensors and functions. One of those is the high limit switch, which helps prevent your system from overheating. When it is not working properly, your system may think it is hotter than it is, causing it to engage safety measures.

What this may look like for you is that your circulating fan may constantly be running, and you will feel cold air being blown out of your registers. The switch is something you want to have a qualified technician replace because it is in the burning chamber of your furnace. Attempting to replace it yourself could cause a gas leak or carbon monoxide leak, both of which are extremely dangerous.

Clogged Condensate Line

During hot and humid weather, your system will create condensation as your air conditioning is running. This condensation drips down, usually into a drip pan, which has a small pipe that allows that moisture to drain. However, it is very common for that line to get clogged with dirt and other grime over time. When this happens, the tray will fill up. Another safety feature is to trip the system and prevent it from running when the tray is full. When you first start your furnace in the fall, you may notice it doesn’t want to run, and this can be a key cause.

Regular system maintenance usually includes cleaning the condensate line to ensure this does not happen. If you have not had regular maintenance, you may want to see if the drip pan is full. When you find it is, check the drain line to be sure it is flowing freely.

Source Fuel Issues

Your system will not be able to run if there is a problem with the source fuel. Your furnace may run on natural gas, propane, or even kerosene. Regardless of what the source fuel is, if it can’t get to your burner, the system will not warm up.

When you try to cycle your system on, listen to what your furnace is doing. If you do not hear the exhaust fan kick on and the burner start, then there may very well be a fuel issue. This is again something you want a trained professional to handle. In this case, it is a licensed plumber who will conduct the repairs. All these fuels are extremely dangerous, so you do not want to risk personal injury or property damage by not knowing how to do the repairs safely.

Problems With Your Ignitor

Depending on your furnace model, you may have a hot coil ignitor or a pilot light. If your furnace is failing to cycle on, another common problem is failure to light it so the fuel coming through can be heated.

In the case of a pilot light, these can sometimes be blown out if the right winds encounter your exhaust pipe. There should be instructions on your furnace for how to relight the pilot if it does go out. However, if your pilot light continues to go out, consult an HVAC professional to troubleshoot more significant problems.

Other furnace models may use a hot coil ignitor to light the fuel. This is usually a ceramic device that uses electricity to warm it up. Once it is warm enough, it produces a signal for fuel to be delivered and be ignited.

Either of these issues should be addressed by a licensed professional. You don’t want to void any warranty that comes with your HVAC system by trying to fix a problem yourself and making matters worse.

Faulty Burner

You may notice a burning smell when you first light your furnace. That can be a big problem caused by dust collecting on the burner surface. This collected dust can cause the burner to clog, preventing it from lighting properly. During a regular maintenance visit, your technician will clean the burner, ensuring there are no issues with it lighting and burning properly.

Malfunctioning Gas Valve

Over time, your gas valve may get clogged, preventing fuel from being delivered to your system. This is a simple maintenance task but can be costly when it is neglected. The best way to prevent this is to ensure you are getting regular maintenance on your system.

Leaky Air Ducts

Another very common issue of colder air coming in from your registers is leaky ducts. These ducts may loosen over time, allowing colder air from unheated areas to enter the system and get circulated with the warmer air. Furthermore, if your ducts are not insulated, you can experience a loss of heat through the ducts between your furnace and the registers.

Have an HVAC professional inspect your ducts to be sure they are still in good working order. Ask about whether you should seal or insulate your ducts. Qualified professionals have diagnostic equipment that will show you how much heat you are losing through your ducts.

Sun City Mechanical has been providing furnace services to the Phoenix area for nearly 20 years. Our team consists of professionally trained HVAC technicians. We also have a team of licensed plumbers if you have plumbing issues. Call Sun City Mechanical today to schedule your repair or to receive more information about our services.