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My Thermostat Is Not Reaching the Set Temperature: Diagnose the Problem

When the winter winds blow in, you want to make sure that your home is going to be comfortably heated. There are many different factors that can influence the temperature in your home, ranging from the placement of your thermostat to the sensor on your furnace.

Every piece must be playing its part perfectly in order for your home to be warm and cozy on those blustery winter nights, but what do you do if the thermostat is not reaching the set temperature?

Here are a few common problems and their solutions so that you can rest easy this winter.

A Dirty Air Filter

If your thermostat is not reaching the set temperature heat, there is no need to panic right away. The issue may not be a difficult one to fix at all. In fact, it may not even require the assistance of an HVAC technician. Before you do anything else, make sure to open your air returns and inspect your filters. You might find that they are completely clogged with dust, pet hair, and other allergens that have been pulled from the air of your home.

This dirty filter can block the airflow into your home, preventing the furnace from heating up all the way. Make sure that you are routinely changing these out with high-quality pleated air filters.

Most people find that they need to replace their air filters once every ninety days or so. However, this number can certainly change if you live in a crowded home, have several pets, or are more sensitive to allergens. Some people change their air filters on a monthly basis to keep them from becoming clogged. Stay on top of this chore to prevent major issues with your thermostat.

While you are working on your air returns, make sure that nothing is blocking them. There should be no furniture stacked in front of them or anything else that can obstruct clear airflow. This will help you to keep your house warmer this winter.

A Broken or Dirty Sensor

It is quite possible that you can repair your furnace all on your own. When you encounter a problem, and your thermostat is not reaching the set temperature, it might be as simple as a dirty or broken sensor on the furnace. In most cases, the flame sensor is more likely to be dirty than broken.

Carbon buildup can interfere with the way the furnace reads the temperature. Unfortunately, most people have a furnace that is located somewhere with lots of dust, such as laundry rooms, basements, or attics. If you have not been diligent about changing your air filters, this can also contribute to the amount of dust that has built up in your system.

Over time, the dust particles make their way into the furnace and stick to the sensor. It heats up and burns them onto it, creating carbon buildup.

Fortunately, this is a problem that you can solve all on your own. First, make sure that you turn off all power to the furnace. This is an absolutely critical step that you cannot afford to miss. If you are unsure how to turn off the power to your furnace, then you need to leave this job to the professionals.

Following the guidelines laid out in your owner’s manual, carefully remove the sensor from the furnace. You may have to disconnect a wire in order to remove it from the furnace entirely. Once it is out, you can take a very light grit sandpaper and gently rub it all over the sensor. Keep in mind that the goal is not to do a full sanding. You simply want to knock off any carbon buildup that has developed.

When finished, wipe it down with a clean paper towel and replace the sensor back in the unit. Turn the power to the furnace back on and give it a few moments to start up again. Give it a while to see if your furnace is suddenly able to keep up with the temperature set by the thermostat. If not, it may need to be replaced altogether.

Wrong Size Unit

Did you recently replace your furnace with a brand new model? A professional should have taken a close look at your home to help you determine the proper size of your new unit. There is a specific formula used to determine the size of your furnace. It incorporates the square footage of your home, the number of occupants, the number of windows, and many more small details. It isn’t as simple as heading to your local home improvement store to pick one out.

Many homeowners are led to believe that a bigger furnace is always the better option. Unfortunately, this is simply not the truth, and it could be the reason that your furnace won’t reach the set temperature. A furnace that is too big will run quickly and heat up the air right next to the thermostat. However, it never warms up the air in the rest of the house quite enough, and it shuts off frequently.

It would be far better for your unit to be slightly smaller and run more consistently to actually heat up your home instead of cycling on and off again frequently.

On the other hand, some people try to scrimp and save on the purchase of an expensive new furnace. You can try to live with a unit that is too small, but you might be facing some pretty chilly winters. A unit that is too small will never be able to heat up a huge home because it simply lacks the power to catch up to the cold.

Poor Thermostat Placement

Does your thermostat say that it is one temperature in your home, even though it feels much cooler in other parts? The problem might have more to do with the placement of your thermostat than with your furnace. The proper placement of a thermostat is crucial if you want your home to be comfortably heated throughout the winter and cooled during the summer.

The right location should be somewhere in the central part of your home. This can be difficult if your house is too large, which we will explore in the next section. It should be located on an interior wall, so it is less susceptible to the fluctuations of the outside temperature. You don’t want it to be too close to any areas of the home with high humidity or steam such as bathrooms and kitchens. Ideally, it would be in an area exposed to high levels of air circulation instead of a closed-off space.

If these descriptors do not line up with the placement of your current thermostat, it may be worthwhile to consider having it moved.

Need a Zoned System

How large is your home? Homeowners who live in fairly large houses may have too much square footage for a single thermostat to control their temperature. There is no single spot that is going to be an accurate reading of all the temperatures throughout your home, particularly if you have an upstairs and downstairs. You might want to consider having an HVAC technician come out to give you a quote on installing a zoned system.

A zoned system allows you to control the temperature for different parts of the home separately. For example, you can tie all of the bedrooms to one thermostat and all of the main living areas to another. This allows you to set two different temperatures throughout the day and gives your furnace a better chance of keeping up.

If your technician does not feel that a zoned system is right for your home, he or she may still recommend installing multiple thermostats. You can install multiple thermostats around your home and connect them so that your furnace reads the average temperature across all rooms. This will help you to reach a more consistent temperature in every room of your home.

Old and Outdated Thermostat

Another reason that your thermostat may not be reaching the set temperature is that it is simply old and outdated. Like any appliance, your thermostat can eventually go on the fritz and need to be replaced. Consider how old your thermostat is before you take any extreme measures to try to repair your furnace or even call in the professionals.

An old thermostat may not be reading the correct temperature in the home. In turn, it cannot send the necessary information to the furnace in order to heat up your home. The furnace may be in fine working order, but it cannot keep your house warm without the proper marching orders from your thermostat.

When it comes time to replace an old thermostat, consider installing a smart thermostat instead. This allows you to have more control over the temperature of your home, automatically adjusting the temperatures for different times of the day. You can even gain access to your thermostat settings from your smartphone so that you can warm up your home in the hours leading up to your arrival and keep it cool while you’re away.

Overheated Furnace

Are you still feeling frustrated that your furnace won’t reach the set temperature? There is a possibility that there is something majorly wrong lurking within your unit. The furnace itself may be becoming too hot to continue to run. It has a failsafe built into the unit that allows it to shut off if it begins to overheat. This is an extremely dangerous situation that should be taken quite seriously.

If your furnace is overheating, then it is likely turning off before the thermostat is able to reach the set temperature.

How do you know if your furnace is overheated? Most people find out when they call in a professional. They take all of the steps that they can try on their own at home first, but nothing simple seems to solve the problem. There is likely a larger culprit that still needs to be identified, but it will take the trained eye of a professional. Don’t hesitate to call your local HVAC company if you suspect that your unit might be overheating.

Iced Over Unit

If your system utilizes a heat pump to keep your home warm and cozy, you may want to head outside and take a closer look. When the temperature dips below 35 °F, the heat pump loses its ability to heat up the home effectively. It instead relies on the supplemental heating system that is usually an electric resistance heater. Once the temperature is restored, the supplemental heat turns off, and the heat pump returns to working on its own.

You might find that the temperature quickly drops again after the supplemental heat turns off, starting the cycle all over again. This is when you might want to take a walk outside.

Colder temperatures might cause your heat pump to actually freeze over. Until the ice thaws, there is little that you can do to get things moving again. This is not something that an HVAC technician is going to be able to correct for you until the temperatures rise again. Simply be aware of the situation and continue to monitor it until it thaws.

Poor Insulation

If the house is not reaching the set temperature, there might be more going on than simply furnace problems. It could be because you are letting in too much air from the great outdoors. This is something that can easily be fixed for a weekend project, and it requires absolutely zero help from a professional.

Many people find that their homes are colder in rooms that have a lot of windows and doors. It can be a good choice to install new weatherstripping or caulking around these areas to keep the outdoor air outside instead of allowing it to filter in and chill your home.

Adding new weatherstripping may not be enough to keep the cold air from coming in through your windows. Make sure to shut them as tightly as possible, but then consider shrink wrapping your windows to insulate them further. This is a surefire way to keep chilly air outside where it belongs. Keep in mind that this means you will not be able to open the windows for any reason, so think it through before you take this drastic measure.

Of course, you might have a more extensive issue with poor insulation. If you think that you might want to explore installing better insulation in your walls or crawl space, it might be time to consult a professional. They can give you better direction on the specific types of insulation available, as well as their general price.

General Repairs

There are a wide number of things that can go wrong between your thermostat and the furnace. If you have already tried all of the things on this list and still cannot get your home to reach the appropriate temperature, then you might need to consider a major repair. While no one wants to handle the financial obligation associated with hiring a professional, it may be your best bet to get the issue resolved as quickly as possible.

Make sure that you are hiring a true professional who has experience working on systems like yours. They should be able to offer you some guidance about other ways to improve the efficiency of your system during their service call as well.

Schedule Routine Maintenance

Even if your thermostat is doing its job just fine, you should still schedule routine maintenance for your furnace. An HVAC technician can come out to make sure that everything is in working order from your sensor to the heat exchanger. With a routine maintenance appointment, you can sometimes spot potential problems on the horizon long before they leave you feeling cold on a winter’s night.

If you find that you aren’t sure what is wrong with your thermostat, you can try some of these simple DIY tricks at home first. Changing your air filter or installing a new thermostat may be the only action that you need to take. However, there is a possibility that you will require more than these simple tasks. If this is the case, consult a professional to take a good look at your overall unit.

Michael Joseph