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At SmartHomePerfected, your safety is our top priority. We always encourage our readers not to take on any tasks that may be beyond their skill set. As such, it’s best to seek the assistance of a professional. 

Thermostat Recovery Mode
Make sure to set the temperature to a comfortable level. The thermostat will take care of the rest.

1. The Thermostat Temperature is Set Too High or Too Low?

Most homeowners are tempted to speed up the cooling or warming process by setting the thermostat to a very low or very high-temperature setpoint.

However, if the thermostat is set unrealistically high or low, the HVAC system may never be able to reach it or might take hours to do so.

This is because the heating or cooling equipment, such as a heat pump or air conditioner with a single stage, runs at its own pace. So if the temperature difference is too wide, the HVAC system will have to work non-stop to achieve it.

Solution: Let Your Thermostat Run at A Comfortable Temperature

So creating a wider temperature difference between the indoor temperature and the thermostat desired setpoint won’t make your HVAC equipment run any faster or stronger. 

Instead, it will run continuously, wearing down the filters and creating unnecessary strain on your system, not to mention the sky-high energy bills you’re going to accumulate when you forget to readjust the indoor temperature.

So the best course of action is not to overshoot. Simply adjust the temperature to a comfortable level with the temperature mode set to heating, cooling, or auto as required. 

Your thermostat will gradually engage the HVAC equipment to achieve and maintain this comfortable temperature without excessive power consumption.

heat pump
It's important the size of the HVAC equipment is large enough to heat or cool the space

2. Undersized HVAC System

If you have a large house, and the HVAC system is not sized appropriately, it can also lead to unattainable indoor temperatures. 

On top of that, the house can get heated up or cooled down unevenly with rooms that are closer to the supply registers reaching the desired temperature sooner while others will remain uncomfortably warm or cold. 

Solution: Upgrade your HVAC System and Optimize the Indoor Temperature Readings

If your HVAC system is undersized, there’s only one possible solution: get an HVAC company to scale up your equipment and vents so the temperature of your entire house can be adjusted evenly.

However, if it’s a problem of temperature differences, you can consider setting up a smart thermostat with remote sensors to prioritize and manage different rooms or “zones” within your house.

Mercury thermostat
Removing the front panel and clearing away any dust or debris can help its temperature sensor read more accurately

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, specifically near the embedded temperature sensor, it will cause the temperature readings to be less precise. 

Also, this can have a big impact on the lifespan of the thermostat making it last less than normal.

Solution: Clean the Interior of Your Thermostat 

You can solve this issue by cleaning the inside of the thermostat enclosure. To do that: 

  1. First, remove the panel of the thermostat. 
  2. Then, make sure you gently clean all metallic contacts with a dry cloth. Avoid cleaning with a wet cloth since it may cause electrical damage. 
  3. Make sure to dust off any vent holes so air can easily flow through the thermostat.
  4. When you’re done, put the thermostat cover back on and give it a run. 
How to Move a Thermostat
Moving a thermostat can solve the problem, but can be a large undertaking

4. The Thermostat is Installed in the Wrong Location

When it comes to reading the average temperature of the room or your entire house, the location of the thermostat can play a huge role. 

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.

Ideally, you want it centrally located or in a common area such as a living room or master bedroom. Excluding the kitchen, of course.

Solution: Move the Thermostat

Sadly, there is no way around it: you have to change the location of the thermostat and this means: moving the thermostat wiring as well. 

However, depending on your skill level and how far you have to move it, this can turn into a major electrical project, so make sure to read this article or get help from an electrician or HVAC expert.

Thermostat Wiring
Wiring can become loose over time, causing thermostat issues

5. Loose or Incorrect Thermostat Wiring

If you just installed a new thermostat but it doesn’t operate the HVAC equipment as it normally should, you may want to double-check your wiring connections. 

If a wire is connected to the wrong terminal, or not connected at all, it can cause the HVAC system to malfunction or not respond.

Solution: Double Check the Wiring

To fix this problem, remove the cover of your thermostat and make sure there aren’t loose wires.

You can check for loose wires by gently pulling them. If the wires come loose, then you need to reseat them and secure them tightly. 

Also, check the thermostat wiring color codes to ensure they’re connected to the appropriate terminals. If you have wired it wrong, disconnect the appropriate wires and rewire them accordingly. 

You can check the user manual for the correct wire configurations.

Temperature and Humidity Sensors
Integrated or external temperature sensor can malfunction

6. Malfunctioning Temperature Sensor

Sometimes the internal temperature sensor of your thermostat may be faulty. 

So, to confirm this, check the room’s temperature through a dedicated thermometer and see if it matches up with the temperature reading on the thermostat. 

This comparison can quickly indicate whether the integrated temperature sensor still functions properly.

Solution: Repair or Replace the Thermostat 

If you come across this problem, the only solution is to replace the sensor. However, in some cases, you cannot replace these spare parts and you might end up having to buy a new thermostat entirely. 

First, check if the sensor can be replaced by the manufacturer, if not, consider replacing the thermostat or going for an upgrade.

Will a Thermostat Work Without Batteries?
Now might be a good time to replace the batteries if you haven't done so in a while

7. The Thermostat Might 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, loose wiring, or just regular wear and tear. 

Solution: Replace the Batteries or Address Any Wiring Issues

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 secure or correctly installed. 

In the end, if none of the above works out, you may want to consider replacing the thermostat.

Nest Reset
Restarting and Resetting is always worthwhile

8. The Thermostat Needs to Be Reset

If your thermostat measures temperature accurately and you still can pinpoint why the system is struggling to reach the desired temperature, it might be a glitch or programming error within the thermostat. 

Solution: Factory Reset the Thermostat

In this case, try to reset the thermostat. Most thermostats have an option for factory reset, which will restore all their settings to default. 

To know how to factory reset your specific model, check the user guide. 

Additionally, you can carry out a reset using the menu (for most Honeywell thermostats) or locate the reset button placed under the thermostat’s cover. 

If you find a reset button, press and hold it for a few seconds. This should reset your thermostat to its factory settings.

If the problem still persists, try removing the batteries as well.

HVAC Filter
Clogged air filters can cause major issues

9. Problems With Your HVAC Equipment

When it comes to your HVAC system, problems such as an undersized HVAC system, clogged air filters, and debris buildup around the heat pump can drastically reduce its efficiency.

These issues prevent your system from reaching the desired temperature, leaving you feeling uncomfortable in your own home.

Solution: Get Help From a Professional

To identify potential issues, carefully inspect each component of your HVAC system for signs of malfunction, such as unusual noises or lights. Additionally, check for dirty fan ducts or pipes that may be inhibiting airflow.

However, digging into the troubleshooting aspects of an entire HVAC system is better left to the professionals. Therefore, I recommend getting the help of a professional HVAC technician who can accurately diagnose and address the underlying issue.

For Mechanical Thermostats

Although these types of thermostats have been widely replaced by digital models, many homes still use them. 

So even if mechanical thermostats can generally be reliable, it's not uncommon for them to have issues with maintaining accurate room temperatures.

So let’s consider 3 additional reasons why your mechanical thermostat would struggle to achieve the desired temperature setpoint.

10. The Anticipator May Be Defective

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 it turns uncomfortable level. Therefore, it predicts the temperature change and switches the furnace on or off as necessary. 

If the anticipator is not working, your thermostat won’t reach the desired temperature setpoint or it might even overshoot without shutting down the furnace.

Solution: Recalibrate the Thermostat Anticipator 

Adjusting, repairing, or replacing the anticipator can fix this issue.

11. The Thermostat is Not Level

Mercury thermostats might measure temperature inaccurately or their regular operations may be interrupted if the thermostat panel is not perfectly square. 

This happens because the slant causes the mercury to always tilt towards one end regardless of the indoor temperature. 

Solution: Make Sure the Thermostat is Level

Make sure the thermostat is in a perfectly horizontal position, and the mercury switch is straightened and leveled. 

You may need a spirit level to check the level along with a drill to re-drill any holes.

Make sure you mark the new holes correctly and use a center punch tool or a loose nail to create a small depression before drilling. 

12. The 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. 

Solution: Recalibrate the Thermostat

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

There can be many reasons why your HVAC system is struggling to meet your desired temperature setpoint. However, almost half of these can be solved right at the thermostat. 

So make sure the thermostat is correctly wired, with a fresh set of batteries, and proper temperature settings.

However, if if the issue lies within the heating or cooling equipment, I recommened calling in the professionals to take a look.


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