Your Furnace Troubleshooting Guide

Forced-air systems are the most common heating method used in the United States. If this is the system you have in your home, then you are getting your heat from a furnace (or a heat pump, but we’re focusing on furnaces right now). Forced-air furnaces are fairly reliable. However, there may be times when you are either noticing insufficient heat, inefficient operations, no heat at all, or other tell-tale signs that something isn’t right. Because of the possibility of the unexpected happening, you’ll want to read on for tips on how to troubleshoot common furnace problems. If you’re experiencing the same problems, it’s best to contact a professional HVAC repair company as soon as possible.

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Why Does My Furnace Blow Out Cold Air?

There are some common causes for a furnace blowing cold air that you may be able to correct yourself before making a service call.

Does your furnace blow hot air, then cold air, and then no air at all? If so, your furnace may be overheated. The cool air is your furnace’s way of trying to cool itself down while operating. It’s likely caused by a dirty or clogged air filter that needs to be changed.

Another common reason for your furnace to be blowing cold air is because the pilot light is out. There are three solutions for this problem:

  • Relight the pilot light (if it stays on, that’s all you’ll need to do!)
  • Be sure that your furnace’s gas valve switch is in the correct position (e.g., in line with your gas supply pipe)
  • The copper rod your pilot light flame hits (thermocouple) needs to be adjusted or replaced (this isn’t a DIY fix if you’re not familiar with how to do this)
Heater blowing out cold air

Why Is My Furnace Leaking Water?

The most common reason for a furnace to be leaking water is condensation, especially if you have a high-efficiency furnace. Units like this have cool exhaust, which produces condensation. You likely have a high-efficiency furnace if your vent pipe is white plastic. Water pooling from condensation could be due to a clogged floor drain or clogged or broken condensation tubing.

With a standard furnace (metal exhaust pipe), you shouldn’t have any condensation. If you are seeing water from condensation with this type of furnace, it usually means the flue pipe isn’t sized correctly. Water leaks around your furnace may also be caused by:

  • A faulty secondary heat exchanger
  • Problems with your humidifier
  • An internal drain system clog (if your AC unit shares an internal drain with your furnace and you’re at a point where you are still using your air conditioning for warmer days)
Furnace leaking water

Why Does My Heater Smell Like Burning Dust When I First Turn It On?

A strong burning dust smell when you first turn your furnace on after a long period of not using it may simply mean that the system is just burning off the dust that has accumulated from the off-season. If this is the case, the smell should go away within a few hours of operation. if it doesn’t, check to see if your filter needs to be changed.

Should you smell an electrical burning odor that would indicate a problem which should be addressed immediately. Turn the system off and call a professional to identify and fix the problem.

burnt dust from furnace

Why Does My Furnace Make a Small Explosion Noise When It Starts?

If you’re hearing a scary “boom” when your furnace starts, it’s definitely not a sound you can or should ignore. Determine which one of these two issues is causing your furnace to make a small explosion noise by standing near your furnace after you turn it on. Pay attention to where the sound seems to be coming from.

Delayed Ignition

Furnace igniting

If you hear a clicking noise like your furnace is trying to turn on before you hear the “boom” sound, it’s likely a delayed ignition problem. This is often caused by dirty burners, too much gas, or too much primary air. This condition is not good for the system and can become unsafe. A well-trained technician can locate and fix the problem before the condition gets worse.

Expansion of Your Air Ducts

Checking furnace air ducts

If the noise sounds like it’s coming from a few feet away from your furnace after it starts and the blower turns on, it may be coming from your ducts. This is caused by too much static pressure in your ducts, which may result from closed vents, dirty air filters, or ducts that aren’t properly sized for your home.

Why Does My Furnace Make Clicking Noises?

Clicking noise usually mean your furnace is trying to start a cycle. With this problem, you may experience a delayed ignition, or you may not get any heat at all if your furnaces’ spark igniter isn’t able to start your pilot light or burners. This means you have an ignition system malfunction, which isn’t a DIY type of repair.

Repairing home furnace

What If I Suspect a Gas Leak?

If you smell natural gas in your home or near your furnace, take immediate action. Turn off the gas supply valve (usually located by your gas meter). Err on the side of caution and evacuate your home. Do not turn on or off any lights while exiting the home. Call the gas company or fire department from a safe location.

Furnace gas leak

Furnace & Heating Maintenance Tips

Keeping a furnace working properly involves some simple steps. The first one should be turn off the electrical and fuel supply. Ideally, it’s best to do routine maintenance before chilly nights arrive in the late summer or early fall.

Start by vacuuming around the blower. Use a small wire brush to clean built-up soot out of the combustion chamber. Then check the exhaust flue for any visible signs of cracks. Your air filter should also be changed once a month. Accumulated dirt can make your furnace work harder than it has to in order to operate effectively.

If it’s possible, it’s a good idea to slide out the fan unit. Use an old toothbrush to clean the blades and your vacuum attachment to get rid of any accumulated dust or debris. Also, apply a few drops of non-detergent motor oil to the oil parts on the motor. You’ll usually find these around the motor shaft (sometimes it’s underneath a cover plate that you’ll have to remove).

If it’s been a while since you’ve had your furnace checked, you may want to consider having a professional HVAC inspection before you get into the habit of doing routine maintenance yourself to ensure that there aren’t any issues that should be taken care of sooner rather than later. A detailed assessment of your furnace typically includes:

  • Checking for gas leaks around your furnace
  • Making sure safety values are operational
  • Checking the heat exchanger for signs of cracks and deterioration
  • Cleaning and adjusting the pilot and pilot assembly
  • Removing and cleaning dirty burners (dirty burners may contribute to poor combustion and shorten the life of your furnace)
  • Inspecting the flue pipe for signs of corrosion or leaks
  • Securing any panels that may be loose
  • Checking and calibrating your thermostat

Some minor issues can be easy do-it-yourself fixes. However, anything that’s out of the ordinary that can’t be corrected by changing a filter or adjusting settings should be handled by professionals. Heating and cooling technicians also have the experience, equipment, and supplies required to accurately diagnose and resolve many furnace problems safely and efficiently. Take comfort in knowing that with proper maintenance and care, most furnaces can last for 20 years or more with only the need for occasional repairs and part replacements.

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