Why Does the Room Temperature Not Match the Thermostat Setting?

The room temperature might not be matching the thermostat setting in case the latter is dirty, unleveled, and suffering from static electricity. You should also check the device’s calibration and wiring as dust can accumulate in the places where wires get connected.

Is there something wrong with your thermostat or is there something else to blame? Keep on reading to find out. 

Related: Why Does Home Thermostat Say HEAT ON But There Is No Heat?

Is It Really Your Thermostat’s Fault?

Before getting inside the thermostat to clean it or fix the wiring, you have to make sure that this smart device is the root cause of the problem.

Get the points mentioned below out of the way before tackling the actual thermostat.

Give the device enough time

A lot of homeowners tend to turn up the thermostat to a higher temperature when they need to heat up the house as quickly as possible. This might seem reasonable if you have just come home to a cold house, right?

Not exactly.

The truth is that the thermostat can’t control how well your HVAC unit works. It simply sets the final temperature and can’t make the system work any faster.

So, all you can really do is give the device enough time to work its magic.

An average home needs around an hour to get from 60 to 70 degrees.

Get the thermostat out of direct sunlight

It is important to make sure that your thermostat can sense the general indoor temperature. 

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But if the device is located next to a window (under direct sunlight), in the kitchen, or close to a fireplace, it is going to think that the house is much warmer than it actually is. 

Place the thermostat on an interior wall, about 5 ft above the ground and away from doors, windows, hallways, and air vents. Ideally, you should place the device toward the center of your home.

Make sure that the thermostat has power

Ensure that the breaker that is powering the thermostat is on (it could have tripped if your home lost power).

A lot of thermostats need batteries to operate and those should be replaced about once a year. Change the batteries and see if that helps.

Check your HVAC filter

The thermostat might be working perfectly fine, but if your air filters are clogged, the hot air won’t be able to get through the system.

Related: Does Furnace Filter Size Matter?

Change or clean the filters to ensure that lack of airflow is not causing the issue. 

Make sure that the HVAC unit has a proper size

Finally, your HVAC unit might simply be undersized, so it is physically impossible for the furnace or air conditioner to make your home warm or cool enough.

Related: What Type of HVAC System Do I Have?

To find out how many BTUs you are going to need for heating or cooling, you should take the square footage of your house and the environmental conditions into consideration.

In general, the maximum size of the system you should buy would be 40% over the BTUs you need for heating and 15% over the BTUs for cooling.

What to Do When Thermostat Is Not Reaching Set Temperature?

If none of the things mentioned above is the issue, then the problem might be with the actual thermostat.

Clean the Thermostat

The only thing that you might have to do to fix the thermostat is clean it. Dust can end up blocking the device’s sensor and heating it up – as a result, the room temperature won’t match the thermostat setting.

Bear in mind that electronic and smart thermostats don’t need to be cleaned inside

A touch-screen programmable device should have a setting for cleaning. If you have a digital thermostat, you can simply clean its surface.

But if you’re a owner of an electromechanical thermostat that has moving parts under the cover, then you would have to clean the inside of the device every now and then.

  • Don’t forget to turn the power to the thermostat off.
  • Remove the cover. Usually, you would have to simply pull the cover down, but some models have screws that hold the cover.
  • To clean the contact points, start increasing the temperature until you see the contacts close (repeat the same manipulation but with decreasing temperature, if your thermostat controls the AC).
  • Slide a piece of paper or even a dollar bill between the contacts and gently move it back and forth. You can also use compressed air to blow away any debris.

Tip: don’t touch the inside of the thermostat with your bare hands – the oils from your fingers can block the sensors.

  • Use a soft paintbrush to remove any dust from the rest of the components.
  • If your thermostat has a bimetal strip, you can clean the thing with a cotton swab that was dipped in rubbing alcohol.
  • Put the cover back on and check if the problem goes away.

Level the Thermostat

Some older models can’t function properly if they are not leveled. 

A mechanical thermostat, for example, usually has a mercury switch and bimetal springs. These components lay horizontally in the device and adjust the temperature, but if the thermostat tilts, the accuracy is going to suffer.

The device might also be poorly mounted to the wall or the actual wall can be uneven.

Remember that the backplate has to be squared to the wall. You can try loosening the screws on the backplate to adjust its position.

Another thing that you can do is remove the thermostat’s cover and balance the glass mercury tube with a small level.

The Thermostat Is Frozen

Static electricity can easily damage any kind of electronic equipment, starting with computers and ending with thermostats.

The touch screen on the device might simply freeze if you have issues with static electricity in your house. At times, homeowners can even see a spark when they touch the thermostat’s screen when the humidity is extremely low.

In such a situation, you won’t even notice, if the system is reaching the right temperature or not. 

Tip: a whole-house humidifier can help you cope with low humidity levels. 

The only thing that you can do apart from trying to increase the humidity in your house is restart the device. Switch the thermostat off, wait for at least 10 seconds, and switch it back on. 

Recalibrate the Thermostat

There are certain circumstances when your thermostat can lose its calibration:

  • If the device was recently installed
  • If the batteries have died
  • If there was an electrical issue
  • A non-programmable digital thermostat can easily be affected by various external factors

It is relatively easy to calibrate a programmable thermostat. If you are sure that there is an issue with the calibration, then you would have to:

  1. Access the calibration menu from the keypad (consult your owner’s manual for more details).
  2. Use the up and down arrows to adjust the temperature. In some models, you would have to adjust the temperature to negative or positive numbers.For example, if the thermostat shows a higher temperature, then you would have to use negative numbers during calibration.
  3. Return to the main screen and check if your manipulations helped.

Redo the Thermostat Wiring

The problem might be with the wiring inside the thermostat.

If you feel like you can fix this issue on your own, then open the access panel and make sure that all wires are attached to the right terminals (the owner’s manual should have a wiring diagram).

While you’re there, ensure that all the wires are in good condition and that all connections are nice and tight.

Bear in mind that corrosion or lint can get in the place where the wiring is plugged. Use a cotton swab to clean these areas.

Replace the Thermostat

If nothing helps, then it looks like the time has come to replace your old thermostat with a newer model.

Brand-new thermostats are much more accurate and are incredibly low-maintenance.

How to Test a Thermostat

To test the accuracy of your thermostat, all you would have to do is tape a piece of paper towel to the wall next to the device and then tape a thermometer to that towel (this will help make sure that the thermometer is not reading the temperature of the wall).

Wait for around 15 minutes and then compare the readings. Bear in mind that the thermostat is rounding off the current reading to one decimal place, so it is normal to see a slight difference in the numbers.