If your thermostat doesn’t turn on the heat it can be very uncomfortable, especially on a cold winter’s night. You realize immediately that if you don’t get it fixed soon, your home will be cold all night and probably for a few days. Your first reaction is to start looking for the contact details of an HVAC professional. But while you are looking for the number, you start wondering whether there is something you can do yourself to address the problem.
Fortunately, there are things you can do to troubleshoot the problem and in many instances, you will be able to rectify the issue yourself. It may be something as simple as a loose connection or a tripped circuit breaker.
There are various reasons why thermostats sometimes do not turn on the heat power. Therefore you might have to troubleshoot quite a few aspects before finding the problem causing the problem in your HVAC system and thermostat.
Some faults are easier to find than others and you can save time if you troubleshoot in such a way that you look at the most obvious possible reasons first. For your convenience, we’ve organized the troubleshooting steps in a logical order, starting with the obvious and “easy-to-fix” possible reasons.
By following these steps you don’t have to waste time with “complicated” troubleshooting procedures while the problem might have been easily solved in one of the first steps.
Step 1 – Check your circuit breaker
We’ve chosen this as the first logical step because a tripped circuit breaker is often the reason why the heat cannot be turned on. And you don’t need to open your thermostat to check for a tripped breaker.
So, check the relevant circuit breakers on your home’s electric board to see whether they all are still on. Generally, your thermostat and the other HVAC devices are not sharing a circuit breaker and therefore you have to check all the breakers.
If a circuit breaker is tripped, reset it. To reset a circuit breaker, you first have to press the switch down and then up into the “on” position. You’ll hear a click sound when it is on again.
After you’ve reset all the tripped circuit breakers, your thermostat might turn the heat on and then you’ve fixed the issue. If you haven’t found any tripped circuit breakers you have to proceed to step 2
Just remember, if one of the circuit breakers related to either the thermostat or any of the HVAC devices keeps on tripping, there is an electrical issue somewhere in the thermostat, the HVAC system or one of its devices. Then, if you are not a qualified electrician yourself, you have to call a qualified electrician to fix the fault.
Step 2 – Ensure that the heating system is switched on
By completing this second step, you just might save yourself a lot of time. Many homeowners can tell you that they have spent quite a lot of time on troubleshooting to only discover at the end that they’ve never checked whether the heating source has been switched on.
The heating system can very easily be accidentally switched off. If maintenance has recently been done on your heating system, the technician might have forgotten to switch the system on again.
Someone cleaning or moving items near the switch might also have accidentally flipped the heating system’s power switch.
If the heating system has been switched off, turn it on again and your problem might be solved. If you have a heat pump, set it to “heat” rather than “cool” or “automatic.”
If the system has not been switched off, proceed to step 3.
Step 3 – Check the thermostat settings
Two important settings on your thermostat can prohibit the thermostat to turn on the heat if any one of them is set incorrectly.
Temperature settings
For a thermostat to turn on the heat, the temperature in the room has to be lower than the set temperature. If for some reason your programmable or smart thermostat has lost its settings and the temperature is now set to a higher level than the temperature in your home, the thermostat will not turn the heat on.
One reason for the incorrect temperature setting may be that you have accidentally changed the setting. The setting could have also been changed or canceled because of a power surge or outage, especially if your thermostat is a hardwired model. It is also possible that an algorithm or software update may have cleared your pre-set temperature.
But whatever the reason for the incorrect temperature on the thermostat, reset or re-program the thermostat, and your issue could be resolved.
Time settings
If the temperature settings are in place and correct, check the time cycles on your programmable or smart thermostat. Perhaps your thermostat is not turning on the heat when you need it to be running because its current time schedule doesn’t allow it.
The same reasons that might change your temperature settings on your thermostat can also affect your time settings. Ensure that the thermostat’s time schedules are still as originally customized by you. If not, re-program your time schedules.
Step 4 – Check the wiring, battery and Wi-Fi connection
Wire connections
Connections on the thermostat
Loose wires or incorrectly connected wires on your thermostat can be the reason why the thermostat doesn’t turn on the heat. So, as the fourth step, we recommend that you inspect the connections.
To check the wire connections you have to remove the face of the thermostat from its base. But before you remove the face to check the thermostat’s wiring and wire connections, turn off the power to your thermostat and HVAC system. Although the thermostat’s wire only carries a 24-volt current, it is always a good safety precaution to turn off the power to the whole system before you start checking or working on your thermostat and other HVAC components.
After you’ve removed the face of the thermostat from the base, inspect all connections and wires. If some wires are loose, re-insert them into the thermostat’s terminals. To re-insert a wire properly, press down the connector button on the thermostat and push the wire as far as it will go.
The wire has been properly installed if the connector button remains in its position when you let it go. By pulling lightly on a wire you can test whether it is securely connected to the terminal.
When you’re satisfied that all the connections are securely in place and correctly aligned, fit the display back to the base.
Then, power on the system and see whether the heating system is running. If the problem persists, you have to troubleshoot further.
Other wire connections
Apart from the fact that loose connections on your thermostat could cause the thermostat not to turn on the heat, other loose wires in the HVAC system and its devices can also influence this function.
Thus, if your thermostat is still not turning the heat on after you’ve taken all the troubleshooting steps, check for loose connections in your whole HVAC system with its devices. Secure and repair all connections where needed.
If you have a Nest thermostat, it is relatively easy to find loose connections. Nest offers their “Tech Info Diagram” feature. With this feature, you can easily find loose connections as it shows a diagram where all the loose connections are highlighted in red.
Thermostat batteries
Built-in battery
The reason why the thermostat is not turning on the heat might be because the thermostat’s built-in battery has gone bad. This may cause the thermostat to power off. Your thermostat’s manual or the manufacturer’s website should give you simple steps to follow to test the built-in battery. If the battery has gone bad you normally will have to replace the thermostat.
Replaceable batteries
If your thermostat has replaceable batteries and they are in the thermostat for a long time already, the chances are good that they have lost all their power. Drained replaceable batteries can prohibit the thermostat to turn the heat on.
Purchase the same type of batteries and replace the old ones. If you’re not sure about the type of battery, check in the manual or online for the detail. After you’ve replaced the batteries, turn on the thermostat again and wait for about an hour to see whether the thermostat has turned on the heat. If it is still not working, you’ll have to keep on troubleshooting.
The thermostat’s Wi-Fi connection
With a smart thermostat, the problem can be a lost Wi-Fi connection. When there is no Wi-Fi connection, or the settings to activate the Wi-Fi connection are not in place anymore, the thermostat cannot communicate with your heating system. Ensure that your settings are correctly set to allow your thermostat to connect with your HVAC devices via Wi-Fi.
Possible causes of the issue other than thermostat-related faults
As shown above, thermostat and wiring faults might be the cause of the interruption of the communication between itself and the heating system, but it might also be that there are other faults not directly related to the thermostat that can cause the problem. Let’s briefly look at some of these other possible causes.
| What to check | Notes on how to rectify |
| If you have a furnace, check whether the pilot light is on | If you have a furnace, it will not turn on if the pilot light is out. To relight the pilot light follow the steps in your furnace’s manual. If you do not feel comfortable trying to relight the pilot light yourself, you’ll have to call a technician. |
| If you have a gas-powered furnace, check the gas supply | A gas-powered furnace needs a supply of natural gas to initiate a heating cycle. Check the gas supply valve and ensure that it is in the “on” position. If you don’t know where to look for the valve, consult your owner’s manual or the manufacturer’s website. |
| Check the air filter | A dirty air filter can impede airflow and when the filter is completely obstructed, the heating system ends up overheating. The safety sensors of most heating systems will stop the heating system from cycling. Turn off the power to your heating system and open the filter-housing door. Slide the filter out and if it’s older than 3 months, or filthy, throw it away and insert a new, clean filter into the housing and close the door. |
| Check the flame sensor | A dirty or blocked furnace flame sensor will cause the heating system not to start cycling. This is a safety feature. Simply clean the sensor and your problem might be fixed. |
| Check the refrigerant charge | An incorrect refrigerant charge in a heat pump will stop the heating system from cycling. A professional technician can measure the refrigerant charge. Note that in the U.S. only technicians licensed by the Environmental Protection Agency should measure and handle the refrigerant. |
| Check for a faulty capacitor | Heat pumps and gas furnaces use a capacitor in the blower and a capacitor has a tolerance level. When a heating system starts short cycling, the capacitor’s tolerance level may be reached. You’ll know that your capacitor is failing if it produces a buzzing sound. A qualified technician can check the capacitor’s tolerance. It is recommended that the capacitor is replaced before it fails. A failed capacitor could cause a blown motor, which is an expensive heating system repair. |
Conclusion
When your thermostat is not turning on the heat, the temperature in your home can become very uncomfortable. Fortunately, the reason for the issue is in many instances easy to find and fix. Most of the troubleshooting and fixing can be done by yourself and you rarely need to call an HVAC technician.
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