5 Simple Common Reasons Furnaces Stop Working AND How You Can Fix Them

A furnace breaking down in the middle of a chilly night is probably one of the worst things that could happen during cold seasons. Being conscious of the typical issues you may face with a furnace and how to fix them can help you prepare and protect your family from awful experiences.

DP common reasons furnaces stop working

There are at least 5 common reasons furnaces stop working. These include the furnace not producing heat or not enough of it, frequent or short cycling, and problems with the thermostat and ignition or pilot control. Some solutions are easy and can be done without professional help, but other issues should be tackled by an expert and trusted technician.

Approximately 85% of American households have some type of natural gas or electric furnace they rely on to heat their homes. The remaining small percentage either use other types of fuels or basically have no heating systems.

As with all mechanical devices, common furnace problems can and will pop up that will prevent them from doing their job. This article aims to prepare you for the worst times and hopefully save you from sky-high repair and replacement costs. 

Furnace Problem #1: Furnace Not Working

It is obvious why we put this problem in the top spot. By “not working” we mean furnaces that aren't doing anything at all. Not a single peep is coming from that beast and you’re in full bummer mode. A heating system that provides no heat at all is a major downer.

There are several simple reasons why your furnace is not producing heat, especially if there are no outward signs of serious issues:

  • The furnace is not getting power. This again may be a no-brainer, but it is one of the most common blunders that hinders furnaces from producing the needed heat. The first basic place you should go to is the ON/OFF switch which is usually somewhere on the unit or someplace on the wall close to it. If it was accidentally switched off (probably because it looks the same as a light switch), the power will not run through it. If the switch is turned on but there is still no power, check your circuit breaker or see if the fuse is blown.
  • The thermostat is not set to HEAT. You may think this is another trivial mistake to make, but unfortunately, it is a pretty common slip. Your furnace is dependent on the thermostat to call the shots on how to operate. If the thermostat isn’t set properly, the furnace will have no reason to initiate the heating process. So, before you go into panic mode, make sure the thermostat is placed in heating mode.

Furnace Problem #2: Not Enough Heating In Home

You can hear the furnace humming and there is some amount of heat that’s coming out, but it certainly is not enough! What could possibly be wrong? The answers may be just simple ones.

  • The thermostat is not set at your desired temperature. The heating process begins and ends with the thermostat. If your comfort level is at 70 degrees yet your thermostat is at 65 degrees, don’t expect your furnace to have a mind of its own and produce the heat you are longing for. This often happens if a thermostat is trying to run a program when you don’t want it to. Either because you’re home when you usually would not be or something has caused the thermostat to run a default program not scheduled by you. Check if the thermostat is in good shape and functional and set your preferred temperature just so.
  • Dirty or clogged filters. Small as they are, dirt in the filters can cause serious problems for the furnace. A buildup of dust can obstruct the steady flow of air which can trigger overheating in the heat exchanger. A weak release of warm air is usually the first sign of dusty filters so make sure to replace them. If left untreated, “not enough heat” will eventually turn to “no heat at all.”
  • Blocked intake or exhaust venting. The most common type of furnace installed today vents with PVC piping to a side vent on the outside of your home. It’s possible during really bad winter weather for the furnace to not work properly because the snow and or ice build up blocks those vents. Go outside and make sure the venting is clear.

Furnace Problem #3: Furnace Shuts ON/Off Quickly or Short Cycling

A furnace that is working properly is expected to cycle at least 3 to 8 times per hour. You are experiencing short or frequent cycling if your furnace turns off before it reaches the temperature you set in your thermostat, only to turn on back again.

What are the causes and cures for short cycling?

  • Dirty flame sensors. There is dirt that inevitably forms inside your furnace as it burns fuel. Neglected over time this can cause the buildup of dirt on sensitive sensors like the flame sensor. If you're the kind of person that is really handy, you could try to clean the flame sensor yourself. But, we recommend you immediately contact your trusted contractor to do it for you. And get your furnace cleaned regularly to avoid these types of furnace problems in the future.
  • Dirty or clogged filters. Again? Yes, again. We’ll quit mentioning it if you quit making us contractors come out in the middle of the night to change your furnace air filter. That blocked filter can trigger overheating in the heat exchanger. Then the furnace stops working due to that overheating. So check your air filter. 

Furnace Problem #4: Thermostat Won’t Work

As complicated as the furnace can get, it is controlled by one tiny, simple device: the thermostat. Conveniently located within your living space, the thermostat is the boss that tells your heating system what and when to do its job. Once you set your preferred temperature in the thermostat, it will activate the furnace to reach your desired level of heat.

Thanks to modern technology, thermostats can be programmed depending on your daily or weekly activities. You can also manage your house’s temperature even if you are miles away if you link your thermostat to your smartphone.

However, these advances may confuse some homeowners if the thermostat mechanism is too complex. Here are the typical issues you can encounter if your thermostat isn’t working.

  • Dead battery. Most thermostats are powered by batteries. If the thermostat isn’t working or the screen is blank, replace its batteries with fresh ones. If you’re not sure where your batteries are at, do a search on Youtube for “(your brand of thermostat) battery replacement”. You’re bound to find a video matching your thermostat that will walk you through the process.
  • Incorrect settings. Like what’s mentioned above, a thermostat set “to cool” rather than “to heat” may sound simple but it can prevent furnaces from producing much-needed heat for the home. Once you switch it to heating mode, compare the current room temperature to the level pre-set in the thermostat which is typically shown side-by-side. Next, set the heat 5 to 10 degrees higher than the room temperature and wait until the change takes effect before turning it up higher to your preferred level.
  • Wrong day and time. This is especially important if you have a programmable or smart thermostat. If you set your furnace to kick in as soon as you get home from work at 5:00 PM from Mondays through Fridays, it is expected to do just that. But if your date and time setting in the thermostat got mixed up, your expectations will not be met. Double-check that your thermostat has the correct day of the week and time of the day. 
  • Damaged wiring. If your thermostat has stopped working after you have done a minor renovation close to where the wiring of the thermostat runs, investigate if there are no broken wires. If the electrical system that connects the thermostat to the furnace gets disrupted, the furnace will not perform well or at all.

Furnace Problem #5: Furnace Ignition Failure Cause

Early model furnaces have a standing pilot light that ignites the furnace with a small blue pilot flame. This type of ignition needs to stay lit at all times.

Newer furnaces brought on the innovation of electronic ignition. This modern lighting automatically turns on when there is a call for heat and off as soon as the burners ignite.

What are the common problems that occur with the ignition?

  • Extinguished pilot light. This applies to old furnaces. The pilot flame could be blown out by a draft nearby. The easy solution is to check for the source of the gust of air and seal it. To relight the pilot light, follow the instructions usually provided on the door of the furnace.
  • A faulty ignition system. If you don’t see any flames when there is a call for heat but the furnace is “trying” to run, you most likely have a problem with the electronic ignition within the furnace. This could be any number of reasons for this failure so better call an expert technician to give you a hand on checking the issue.
  • Dirty flame sensors. Again with the dirty flame sensors! If you notice the furnace lighting but only staying lit for a short time, it could be a problem with a dirty sensor. Again, we recommend you immediately contact your trusted contractor to get this checked out. And get your furnace cleaned regularly to avoid this one in the future.

Bonus Common Furnace Problem: Furnace Not Working After Changing Filter

There are two common reasons for the furnace to stop working after changing the filter.

  • Door Switch Safety. If you have to remove a furnace door to replace your filter, it's possible that if the door is not put back on securely that the furnace will not operate. This is due to a safety switch that prevents the furnace from running with the doors off. Recheck the furnace doors to make sure they are properly installed.
  • Restrictive air filter. Sadly, some new filters that are being sold today cause more harm than good. Due to current rating standards, a high end (and high cost) filter can be sold that is advertised to be extremely efficient. These filters claim to be better for catching allergens, viruses and a host of other bad guys you don't want to breathe.

    The problem is they do this without letting the proper amount of air pass through them. In other words, the new "high end" filter you just bought from the big box store acts like a clogged air filter that's completely blocked, restricting the airflow to the furnace.

    The best thing to do if you have one of these new filters is to return it to the store and buy a simple filter that costs a few bucks. If you want to use a high efficiency filter you'll need to get one installed by a good contractor that is designed to catch the dirt AND let air through it.

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