When your furnace stops working, you notice pretty quickly during the winter months. Generally, your system will have either stopped running altogether or it will have started blowing cold or room temperature air around. There are few different ways to troubleshoot problems with a furnace, depending on the type of heating system you have. Many of the problems are easy for a homeowner to address themselves without calling in a professional. We’ll walk you through some of the basics.

General Troubleshooting     

Start at your thermostat:

– Is the system switch or button in the “heat” mode?

– Is the temperature set at least 3-5 degrees above the actual room temperature?

– If you have a digital thermostat is the display working? Some thermostats are battery powered and should say so somewhere.

If you have no display and fresh new batteries are not the problem you more than likely have no power to your heating system. If able to, turn the fan to the ‘on’ position to check for power. If you don’t hear anything or feel air movement you could have no power to the unit. Be sure to check your wall switch and all of your circuit breakers for correct positions.

Your wall switch is typically a regular light switch located on either the side of the furnace or near the door to the room. When checking your circuit breakers look for any that look like they are in the middle position between ‘off’ and ‘on’. Even though this is how it usually works sometimes breakers will trip and not move at all. So for good measure locate the breaker labelled ‘furnace’ or ‘heat’ and turn it off, then back on to reset power. This can reset any fault codes your system may have detected so make sure you have checked for those before you do this, read on below.

Types of Heating Systems

If your system is getting power, identifying which type of heating system you have is the first step in helping you figure out what the problem could be. The three most common types of heating systems are:

  • conventional gas or oil furnaces
  • hydronic boilers
  • heat pumps

Troubleshooting a Conventional Gas Furnace

Efficiency Rating

If you have a conventional gas furnace, you need to know its efficiency. This can generally be determined by the type of venting that’s used. Furnaces with 90% efficiency use PVC pipe for venting because it reuses most of its flue gas to heat the house. Because of this, the exhaust a 90% efficiency furnace produces is cool enough to be vented with PVC. Furnaces with 80% efficiency use metal venting because there’s more gas in the exhaust. When the system is running properly, the pipes get extremely hot when being used in heat mode. For this reason, metal pipes have to be used with lower-efficiency systems.

Check Air Filters

Regardless of its efficiency, the first thing that needs to be checked on a conventional gas furnace system is the air filters. If the filters are dirty and clogged, air can’t circulate throughout the home.

Get Diagnostics Codes

If the fan is blowing cool or room temperature air, check for a diagnostics code. Most furnaces rated 80 & 90 have an LED code that flashes through a small circular window.  If you count the number of times the light flashes, it will signal a diagnostics code you can use to figure out the problem.

Other Issues

If everything comes on, including power and gas, but the furnace doesn’t ignite, you’ve likely got a bad ignitor or circuit board.  If the flames come on, but turn off again within a few seconds, the cause could be either a dirty flame sensor or low gas pressure. Either way you are probably going to have to call a professional as most parts these days are factory specific and acquired locally. Gas pressure is one of those things that should be checked regularly anyway to keep a properly maintained system.

Troubleshooting a Boiler

Boilers use hot water pipes that circulate throughout the house to heat, so these systems don’t require air filters. Boilers do have a circulator pump that must run in order to circulate heat. If heat isn’t circulating, you may have a problem with the circulator pump. Air locks in the pipes can also keep certain rooms from heating.

Troubleshooting a Heat Pump

Heat pumps use electricity and refrigerant to heat and cool. Like furnaces, they use air filters that must be clear of debris in order for air to circulate properly. Heat pumps have relays and contactors that must be working properly. These run on fuses that can blow. Heat pumps can also build up ice on the outside unit which can cause problems if it’s not defrosted from time to time.

If your heating system uses a gas furnace or a heat pump, be sure to use high-quality air filters and change them regularly to keep your system working efficiently.

2 thoughts on “What To Do When Your Furnace Stops Working

  1. Lillian Schaeffer says:

    This is some great information, and I appreciate your point that your furnace not igniting should be looked at by a professional. Everything else on my furnace is working fine, but it either won’t ignite, or it will go out again after a moment. I’ll definitely look into having a professional come and take a look to see if it needs to be repaired. Thanks for the great post!

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