The Most Common Furnace Problems and Their Solutions

The furnace is one of the most hard working and useful household equipment. Unfortunately, many people do not realize the importance of their furnace until it stops working. Furnaces fail due to many reasons ranging from lack of maintenance to improper use.

A malfunctioning heating system in Sacramento can stop working anytime, leaving you high and dry. A faulty furnace can release CO, causing CO poisoning. If you continue using a faulty furnace, it will develop issues frequently and you may end up spending a fortune on repairs.

Here are some common furnace issues and their solutions.

Furnace Blows Cold Air

Returning from work, expecting a warm home to find out that your furnace is blowing cold air could be a harrowing experience. Here are some reasons why furnaces blow cold air.

  • Thermostat issues: Check your thermostat to see if it is working properly. Your batteries should have enough juice to last at least a couple of months. Clean your thermostat and make sure it is placed in an area that does not receive direct sunlight
  • Pilot light won’t turn on: Old furnaces have a pilot light that ignites the fuel inside. An unlit pilot light is an indication that your furnace is no longer working. If your pilot light does not turn back on after following the owner’s manual steps, seek help from a trained professional
  • Dirty air filters: Dirty air filters could do more harm than good. Unclean filters are the number one cause of airflow problems. Filters should be changed every 90 days (more frequently-every 30 days if you have pets, kids or elderly adults at home)
  •  Clogged condensate line: High efficiency furnaces have condensate lines that move water away from them. Sometimes, the condensate line becomes clogged, preventing the furnace from igniting. No ignition means only cold air coming through furnace vents
  • Leaky Air ducts: If there are holes in your air ducts, the conditioned air may escape through them. The problem could occur due to age related deterioration or when a pest bites or claws at your ducts. If you notice drafty ducts in your home, have an expert come assess the issue right away

Furnace Does not Turn off

If your furnace does not turn off, you might be dealing with a broken thermostat or the blower might not be working properly. Check your thermostat’s setting. Make sure it is set to auto.

If you are using the right setting, pull your thermostat out of the wall and check it for frayed wiring. All the wires should be securely connected. Repair or replace damaged wiring and/or tighten loose connections. Restart the system to see if the problem is resolved. If the problem persists, call a trained professional.

Furnace Short cycling

It’s normal for a furnace to turn on and off about 2-3 times every hour. If your furnace turns on and off more frequently (short cycles), you might be dealing with a serious heating issue.

Here are some causes of furnace short cycling.


If your furnace overheats, it will automatically turn off. The built-in mechanism is designed to prevent damage to the system and the motor.

Some common causes of furnace short cycling are clogged air filters and blocked furnace exhaust pipes. Check your air filters and replace if required. Make sure the supply and return vents in each room are unblocked.

Dirty flame sensor

A furnace’s flame sensor is designed to ensure that gas flows into the furnace only when a flame is present (to prevent gas from building up). When the flame sensor does not detect a flame, it stops the flow of gas.

Over time, your flame sensor can get dirty. If it gets too dirty, it won’t be able to detect a flame and automatically stop the flow of gas, causing your furnace to short cycle.

Your are using an oversized furnace

When it comes to furnaces, bigger is not better. An oversized furnace will provide warm air to your home at a faster than normal pace and will shut off before completing its cycle. Short cycling can cause your system to fail prematurely. If you are planning to buy a new furnace, have your contractor perform a furnace sizing calculation.

Incorrect Thermostat Placement

A thermostat should be installed in a central location. If your thermostat is placed close to a heat source (such as a household appliance), it will turn off frequently. Do not place your thermostat in an area that receives direct sunlight or above or below a return vent or it will determine that your house is too warm and instruct the furnace to shut off.

Uneven Heating

This is one of the most common and frustrating heating issues. If some parts of your house feel warmer than others, you might have a dirty filter (which is impeding airflow) or faulty ductwork.

Some other common causes of uneven heating are blocked or closed air vents, damaged zone controls and lack of maintenance. Have your contractor inspect your furnace before things take a turn for the worse and you end up with a costly repair.

Inadequate Heating

If your furnace does not heat enough, either you have a clogged air filter or you are not using the right size furnace. Other possibilities include a mis-calibrated thermostat or faulty ductwork. If your furnace is not heating adequately, have your technician inspect your system.

South Placer Heating and Air is a leading HVAC company in Sacramento. Our pros have years of experience installing new systems and maintaining and replacing existing heating systems in Sacramento. To talk to one of them, call (916) 246-2089.