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Are you setting a temperature on your thermostat, but the room temperature does not match it? There can be a number of reasons for this. Chances are the problem lies in your thermostat, however, you should take an organized approach to troubleshoot.

Start with the easiest and most probable solution and work your way up to more complicated issues. With that in mind, we’ve created this guide to help you through the process.

At SmartHomePerfected we always advise readers not to undertake any work they are not competent in performing and if in any doubt, it is best to seek the assistance of a professional.

1. Is your thermostat set too high or too low?

A big percentage of homeowners are tempted to speed up the cooling or the warming process by setting the thermostat to a very low or very high temperature value. If the thermostat is set unrealistically high or low, the HVAC system may never be able to reach it.

The reason is that an air conditioner works to create a temperature difference between the outside and the inside. If this temperature difference is too big, the AC might not have the power to maintain it.

This will also make your HVAC equipment run for a longer time, which can cause malfunctions and higher energy bills.

2. Size or number of thermostats

If you have a large house, the thermostat can be too small to cover the entire area of your home. This can result in having cooler or warmer spots in various places, like in rooms that are too far from the thermostat. So how can you keep a uniform temperature all over the place?

Solution: The best way to go is to replace your existing thermostat with a more powerful version that can tackle a larger area of your home. If you have a smart thermostat, get more sensors and hook them up with the thermostat. Otherwise, you can create multiple zones throughout your house by installing additional thermostats. 

3. Thermostat is dirty

Another common reason for inaccurate thermostat performance is the accumulation of dirt in their interior parts. Once dust or debris gets inside the thermostat, it will affect its sensing capabilities and the temperature readings will be less precise. Also, this can have a big impact on the lifespan of the thermostat making it last less than normal.

Solution: Cleaning the interior parts of your thermostat can solve this issue. To do that, remove the panel first. Then make sure you gently clean all metallic contacts with a dry cloth. Cleaning with a wet cloth may cause electrical damage. When you’re done, put the thermostat cover back on and give it a run. 

4. Thermostat's location

The thermostat’s location can be an influencing factor for not reaching the desired temperature. For example, if the thermostat is too close to the ground, near windows or doors, in direct sunlight, or in any place that does not accurately reflect the temperature of your home it may not function properly.

Solution: Unfortunately, there is no way around changing the location of the thermostat. The best solution is to reinstall it in a suitable place. Preferably, place the thermostat near the center of your home taking into account the spaces or rooms you frequently use. If you’re planning on moving your thermostat, you can read up on it here.

5. Thermostat Wiring

If you just installed a new thermostat but it doesn’t reflect the real temperature, you may want to check how you wired it. If a wire is connected to the wrong terminal, or not connected at all, it can cause serious problems to the entire HVAC system. 

Solution: To fix this problem, remove the cover of your thermostat and make sure there aren’t loose wires. The next thing to do is to check whether all wires are connected to the correct terminals. If you realize you have the wrong wiring, remove all wires and start rewiring your thermostat accordingly. You can check your wiring by giving our wiring guide a read.

6. Malfunctioning Sensor

Sometimes the temperature sensor of your thermostat may be faulty. Check the room’s temperature through a traditional manual thermometer and see if it matches the thermostat temperature. This comparison can quickly indicate whether the integrated temperature sensor still functions properly.

Solution: If you come across this problem, the only solution is to replace the sensor. However, in some cases, you cannot replace only spare parts and you might end up having to buy a new thermostat. Depending on which type of thermostat you have, check if the sensor can be replaced with the manufacturer.

7. Factory Reset the thermostat

If your thermostat problem is not apparent, it might be a specific device malware that is causing your thermostat to not operate normally. In this case, try to reset the thermostat. Most thermostats have an option for factory reset, which will restore all its settings to default. 

Solution: The factory reset button is usually placed under the thermostat’s cover. Of course, this can vary from model to model. Once you have identified the reset button, press and hold for a few seconds. This should reset your thermostat to its factory settings. If the problem still persists, try removing the batteries as well.

8. Thermostat may be losing power

If your thermostat display is fading, it is a clear sign that the thermostat is losing power. This can be caused by battery problems, wiring, or just wear and tear. 

Solution: The easiest thing to do is to replace the batteries of the thermostat. If this doesn’t fix the problem, check if the wiring is done correctly. In the end, if none of the above works out, you may want to replace the thermostat.

9. Problems with your HVAC equipment

Issues like clogged air filters and debris around your heat pump can reduce the effectiveness of your HVAC system. As a result, the specified temperature is not being hit. 

One of the components in the HVAC system may be malfunctioning, or the fan ducts/pipes could be too dirty to pump enough air. Closely observe each component and see if they turn on, blink, or show any abnormalities. 

Solution: The best solution is to call an HVAC technician who can determine what is causing your system to malfunction.

For Mechanical Thermostats

1. Anticipator may not be working

The anticipator is a small metal piece installed on a dial inside a mechanical thermostat that is responsible for operating the furnace. As the name suggests, the anticipator anticipates the temperature in a room before reaching discomfort and turns the furnace on or off accordingly. If the anticipator is not working, you may not reach the desired temperature set on your thermostat.  

Solution: Adjusting the thermostat anticipator can fix this issue. Watch this video to get a clear understanding of how to make the right adjustment. 

2. Thermostat is uneven

Mercury thermostats might be disturbed if they are uneven, giving an inaccurate temperature reading. This happens because the slant causes the mercury to flow towards one end regardless of the temperature. Make sure the thermostat is in a perfectly horizontal position, and the mercury switch is straightened and leveled. 

3. Thermostat needs to be re-calibrated

There are situations in which mechanical thermostats lose their calibration because of old batteries or electrical issues. Even newly installed thermostats may require additional time to settle in, despite being calibrated. 

To recalibrate your thermostat, check the user manual provided by the manufacturer and follow the given instructions. You can also try replacing the batteries or consider shifting to a digital thermostat that does not require calibration.

The Verdict

As you can see, many factors can influence the way your thermostat works. Carefully observe and identify what is causing your thermostat to malfunction. Try the solutions presented in this article and, if you still find yourself not being able to fix the issues, consider calling an HVAC technician to investigate and diagnose the situation. 


Lennox HVAC

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