Have you ever wondered what is the most basic, but also the most essential “spare parts” to keep in your home to quickly rectify possible simple issues that might occur in your HVAC system, especially the thermostat? 

If you have a Honeywell thermostat that runs on batteries, the most important “spare parts” will be a set of fresh batteries. If the thermostat’s batteries are depleted, or one of them has gone bad, your thermostat, and thus the whole system, will not work.  So, apart from always having fresh batteries available, it is essential that you know where the batteries are stored in the thermostat and how to replace them.

In this article, I’ll discuss various aspects you have to be aware of regarding thermostats and their batteries, and I’ll also provide you with step-by-step guidelines on how to replace the batteries.

Do all Honeywell thermostats use batteries?

Although most Honeywell thermostats run on batteries, some models get their power directly from the main power supply and don’t use any batteries, except in some instances as a backup power source.  

In this article, I’ll only discuss Honeywell models which run on batteries and briefly refer to thermostats where the batteries are only for backup purposes. 

Preparation steps to take to always be ready to replace your thermostat’s batteries

If you are well-prepared, flat thermostat batteries should not be a problem. 

Preparation: Step 1 – Verify whether your thermostat needs batteries

The first step you have to take is to verify whether your thermostat runs on batteries or not. If you don’t know, refer to your thermostat’s manual or check on Honeywell’s website with your model’s name and serial number.   

As a rule of thumb, a thermostat with an LED display usually works on batteries.   

Preparation: Step 2 – Ensure that you know where to locate your thermostat’s batteries

All Honeywell thermostats that require batteries store them within the control panel itself.  Some thermostats use battery compartments or trays, while others require that you remove the faceplate to access the batteries. Your next step is to locate the batteries.

For your convenience, I’ve made a list of where the batteries are located in the different Honeywell thermostat series.   I indicate whether they are stored in a battery compartment/tray or whether you can only access them by removing the faceplate of the thermostat. 

Honeywell Thermostat Series Battery Location
1000 Series The batteries are located under the faceplate. The faceplate has to be removed to get access to the batteries 
2000 Series The batteries are located under the faceplate. The faceplate has to be removed to get access to the batteries.
3000 Series The batteries are located under the faceplate. The faceplate has to be removed to get access to the batteries.
4000 Series The batteries are located under the faceplate. The faceplate has to be removed to get access to the batteries.
5000 Series The batteries are in an outside battery compartment/tray. You don’t have to remove the faceplate to access the batteries.
6000 Series The batteries are in an outside battery compartment/tray. You don’t have to remove the faceplate to access the batteries. 
8000 Series The batteries are located under the faceplate. The faceplate has to be removed to get access to the batteries.

Preparation: Step 3 – Verify how many and what type of batteries your thermostat needs and buy them

The third step is to ensure that you have the right replacement batteries ready. The different Honeywell models don’t all use the same batteries. 

To assist you in determining what type and how many batteries are needed, I’ve compiled a list for you to use as a guideline. 

Honeywell Thermostat Number of Batteries Battery Type
1000 Series 2 batteries AAA
2000 Series 2 batteries AAA
3000 Series 2 batteries AA
4000 Series 2 batteries AA
5000 Series 2 batteries AA
6000 Series 2 batteries AA
8000 Series 3 batteries AAA

How will you know that you have to replace the thermostat’s batteries?

Usually, your Honeywell thermostat will warn you when the batteries’ level of power is getting very low. The Honeywell thermostats which need batteries to work, all have some form of indication for when the batteries are running low.

If the thermostat uses a screen, you will see a warning which reads something like “Low Battery.”  By checking the screen at least once a day, you will receive an alert early enough to give you time to replace the batteries.  

If your thermostat doesn’t have a specific battery health indicator, it will flash the snowflake icon when the batteries are low. 

Sometimes when the battery power is running very low the screen can go blank to save some power for the rest of the system to keep on working. 

Generally, you only have to replace Honeywell thermostats’ batteries about once every twelve months. It is good practice to replace the batteries once a year in any case, even if you haven’t received a warning from the thermostat. Then you can rest assured that the batteries will most probably always have enough power for the system to function.

Most Honeywell models will start giving you a low-battery alert about two months in advance before it is estimated to receive no power from the batteries anymore.  This is to give you enough time to purchase batteries in time. 

The question you might have now is why you need spare batteries in your home if you get an alert two months in advance. The one answer is that although you are being warned, you might just forget to buy batteries, and one day you suddenly have a thermostat that is not working due to flat batteries.  If you have spare batteries in your home, you can immediately rectify the problem.

Another reason for keeping fresh batteries in your home is that there is always the chance that one of the batteries can, without any warning, just go bad. The thermostat will immediately shut down and if you have a set of batteries handy you can get everything up and running again very quickly.

Guide on how to replace the thermostat’s batteries

In principle, it is very easy and straightforward to replace your thermostat’s batteries. You just put off the power to the thermostat, take out the old batteries, put in the correct new batteries, put everything back, and switch the thermostat on again. 

Each Honeywell Series has small variations in the procedure, and therefore I provide you with this Quick Guide.  

Honeywell Series Steps to replace batteries Do you have to remove the faceplate?
Series 1000 and 2000 Switch off the thermostat. Cut the power to the thermostat and HVAC system completely by putting off the applicable circuit breaker When there is no power flowing to the thermostat, remove the faceplate which is attached to the base. Always pull it from the bottom side and it will easily come off. Remove the old batteries and clean the battery holder. Make sure there is no moisture or any other substances that can influence the working of the batteries. Replace the old batteries with new AAA batteries. Ensure that you place them correctly in the “+” and “-“terminals. Place the cover back on the base plate and ensure that it fits correctly on the base. Turn on the power to the thermostat.
To replace the batteries you have to remove the faceplate from the base.
Series 3000 Follow the same procedure as with the 1000 and 2000 series. The only differences are that you have to push and pull to separate the faceplate from the base, and you have to use AA batteries and not AAA batteries. To replace the batteries you have to remove the faceplate from the base.
Series 4000 The procedure is exactly the same as for the 3000 Series. To replace the batteries you have to remove the faceplate from the base.
Series 5000 Switch off the thermostat Press and simultaneously gently pull the cover to remove the battery compartment/tray which is located at the top right corner. Remove the battery compartment and replace the AA batteries. Ensure the batteries are correctly placed in the proper “-“ and “+” terminals in the battery compartment. Place everything back again. Switch the thermostat on again. It features a sliding battery compartment/tray. Thus, you don’t have to remove the faceplate to replace the batteries.
Series 6000 Turn off the thermostat and remove it from the circuit breaker Press and gently pull out the cover from the bottom and remove the battery Slide out the compartment or tray for the batteries and replace the older batteries with new AA batteries Place the batteries in the proper “-“ and “+” terminals. Place everything back again. Ensure the batteries are placed in the right + and – terminals in the battery compartment or tray. Once replaced, turn on your Thermostat
It features a sliding battery compartment. Thus, you don’t have to remove the faceplate to replace the batteries.
Series 8000 Switch off the thermostat and cut the power to the thermostat and HVAC system completely by putting off the applicable circuit breaker(s). When there is no power flowing to the thermostat, remove the faceplate which is attached to the base. Always pull it from the bottom side and it will easily come off. Remove the old batteries and clean the battery holder. Make sure there is no moisture or any other substances that can influence the working of the batteries. Replace the old batteries with new AAA batteries. Ensure that you place them correctly in the “+” and “-“ terminals. Place the cover back on the base plate and ensure that it fits correctly on the base. Turn on the power to the thermostat.
To replace the batteries you have to remove the faceplate from the base.

Why is everything working after replacing the batteries, but the warning indicator is still on?

Although the battery indicator or low-battery message on the screen should disappear within a few minutes after you’ve replaced the batteries, it is not uncommon for the battery indicator to stay on even after you’ve replaced the batteries. 

If the indicator stays on, the system may require a restart. With a restart, the indicator will be reset. If you have an advanced Honeywell model, you will be able to reset your thermostat by following the prompts and steps on the display menu. 

Some advanced systems can even be reset by using the Honeywell smartphone app. However, to use this option, you must have a Wi-Fi-equipped thermostat system.

If your Honeywell thermostat does not have a reset option in the control panel menu, you’ll have to power it down completely by turning the thermostat’s circuit breaker off. 

After all the power to the thermostat has been cut, remove the batteries from the thermostat control panel. Remove the batteries, even if they are the fresh batteries you’ve just put in. Wait for about two minutes and place the batteries back again and close the thermostat. 

Then turn the circuit breaker on again. This procedure should have reset all the Honeywell thermostat systems and deactivated the low battery indicator.

What must I do if my Honeywell thermostat doesn’t work at all after the batteries have been replaced?

There are various reasons why your thermostat doesn’t work after replacing the batteries. Let’s have a look at the most common reasons and how to rectify the issues. 

The faceplate or battery compartment/tray has not been replaced correctly

When troubleshooting a thermostat that is not working after the batteries have been replaced, you should always start by checking whether the faceplate or the battery compartment lid or tray has been put back correctly on the control panel. For the thermostat to turn on, the pins in the control panel have to make proper contact with the baseplate. 

If you’ve found that the faceplate or battery tray has not been fitted correctly, remove everything and put it back correctly. This could be the solution to the problem.

Batteries might be installed incorrectly

When you’ve replaced the batteries, you could’ve accidentally put them in with the wrong orientation. Carefully remove the batteries and insert them again. Ensure that the batteries are placed in the proper “-“ and “ “+” terminals. 

This could solve the problem. 

Batteries might be faulty

If the problem persists, it might be because you unknowingly have used faulty batteries when you’ve replaced the batteries.

To test whether this might be the problem. Take out the batteries and replace them with another set of fresh batteries. 

If you don’t have extra batteries available, take out the batteries and put them into another device that is using the same type of battery, and check whether the batteries work sufficiently in this other device. If not, at least one of the batteries is faulty.

Conclusion

Most of Honeywell’s thermostats require batteries to power the thermostat control panel. The thermostat and HVAC system cannot function when there are no batteries installed, or the batteries are flat or faulty. 

Generally, it is easy to rectify a flat battery issue, but it is important that you know when and how to replace the batteries safely without damaging the thermostat or any other device in the system. 

Always remember that the entire function of the system relies on two or three small AA or AAA batteries.

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