Furnace Troubleshooting Guide

The inside of a furnace.

A properly working furnace is essential when the cold weather arrives. While furnaces are great for keeping houses warm and cozy, they require regular maintenance and upkeep to ensure they work correctly. From a busted blower to thermostat problems, here is a guide on how to troubleshoot the most common furnace issues.

Blown-out Pilot Light

From drafts to dirty gas tubes, there are a few reasons why pilot lights go out. If the pilot light in your furnace has gone out, check your manual on how to relight it. When relighting a pilot light, make sure the area you are working in has plenty of ventilation. If you smell a gas odor, then call a professional to handle the situation. If the pilot light keeps blowing out, then you probably have a clog somewhere in the gas line.

Furnace Is Not Heating Properly

A furnace's filter.

A furnace that does not blow hot air is useless in the wintertime. If you are having this issue, ensure the unit has power. A blown fuse can disrupt normal operation. Next, take a look at the filter and change it if is dirty. If the furnace still is not working, inspect the pilot light and confirm that it is on. You can also see if the unit has a reset button, which can sometimes fix the issue. If none of these steps work, the thermostat on the furnace may not be functioning or the flame sensor is clogged up.

Noisy Furnace

The kind of noise your furnace makes can tell you a lot about what is going wrong. If it sounds like something metal is scraping, then you are probably dealing with a blower wheel malfunction or a damaged motor mount. A thumping noise usually relates to the blower wheel as well, while a squealing sound is likely a loose belt. Applying some lubricant to the belt will usually fix the issue. If you hear banging coming from the furnace, you might be dealing with a clogged filter or a duct that is too small for the unit.

Blower Not Working

Fixing a broken furnace blower is easier than you might think. The two most common reasons behind blower issues are an improper thermostat setting and a bad fan control switch. For the thermostat, make sure it is not set to continuous as this will cause the blower to keep working when the furnace turns off. When it comes to the faulty fan limit switch, resetting it might fix the issue. If the blower continues to run after reset, the switch should be replaced with an original part.

Thermostat Issues

A man adjusts a thermostat.

Installing the wrong type of thermostat can create many problems with your furnace. Before you purchase a new thermostat, make sure it is compatible with your furnace and vice-versa. In general, there are three varieties of thermostats on the market: line voltage, low voltage, and millivoltage. Consult the furnace’s manual to ensure you are using the right thermostat.

Furnaces Switches On Too Much

A furnace that is turning on too frequently can cost you a lot on your monthly energy bill. A common reason behind a short cycling furnace is a broken thermostat. Before you call in a professional or order a replacement, make sure the thermostat is set to heat. If the thermostat is working, check the flame sensors for rust and corrosion. If those checkout you may be dealing with a dirty air filter, which can cause the furnace to shut off prematurely.

Regular Maintenance

Regular maintenance on the furnace can increase its longevity and keep it working as efficiently as possible. You should check the air filter throughout the year and replace it whenever it gets dirty. It is also recommended to clean out the blower on an annual basis. You can accomplish this by simply vacuuming the blower and cleaning the fan blades. While you are cleaning the blower, inspect the motor’s oil ports. Apply a few drops of oil to the ports to keep the motor lubricated.