How To Change The Battery In An Old Honeywell Thermostat

I was quite amazed when I first found out that there are so many different types of thermostats that Honeywell is selling. There are simple dial, switch controlled, and programmable thermostats. All have different functions and cater to different needs.

Some of these thermostats require batteries to run while others don’t. Most of the thermostats use AA, AAA alkaline batteries, or 3V lithium batteries. With so many types of thermostats available, it is not surprising when one gets completely baffled about how to change the battery in these devices.

This article focuses on old Honeywell thermostats that the company has discontinued already and have provided the users with their replacements.

The Function Of The Thermostat Batteries

Thermostat batteries are used to simply to save the programming of your thermostat. It prevents the heating and cooling control system from switching off when there’s a power outage.

In most Honeywell thermostats, the battery functions as a backup system when the thermostat is not acquiring 24V power from the heating system. If the battery runs out and your thermostat switches off, you do not lose your programming settings. However, you lose your thermostat’s date and time settings.

Indication To Replace The Thermostat Battery

The thermostats that have batteries are the programmable thermostats with an LED screen. If your Honeywell thermostat has an LED display and it is running out of battery, it usually displays the low battery warning sign.

The warning appears like a flashing banner that says “Batt Lo” or “Replace Battery.” If you have failed to notice this warning sign, your last warning will be the blank screen of the thermostat before it goes off.

How Often You Should Replace Your Thermostat Batteries

It is recommended to change your thermostat batteries annually. But you may also replace the batteries at the start of the winter season because of high usage.

Also, if the display screen shows a low battery warning, it’s time for you to replace the thermostat batteries. Even if you own a hardwired thermostat, it might still have a battery for backup which you have to change periodically.

If you live in a place where the temperature drops below freezing point, you should change the batteries before going out of town. It helps to prevent frozen pipes and also to maintain the indoor temperature.

If thermostat switches off while you are away, and below freezing point temperatures can burst the pipes. This can cause a lot of financial expense due to property damage and repairs.

Importance of Batteries in a Honeywell Thermostat

If the batteries in your Honeywell thermostat are dead, your thermostat will not work. The thermostat is unable to remember the temperature settings if the batteries are dead.

It also prevents the thermostat from switching the heating and cooling system on or off. You will also be unable to change the temperature if your thermostat’s battery has died. Batteries also help the thermostat to keep its settings safe when the power goes out.

Battery Replacement in the Honeywell 2000 Series – TH2110D and TH2210D

The Honeywell Thermostat 2000 Series includes the TH2110D and TH2210D models. Honeywell discontinued the TH2110D model on Nov 30, 2014, while it discontinued TH2210D model on April 25, 2014. These thermostats have a display screen and dial-control buttons.

These models are feasible for normal heating or cooling systems and heat pumps. The thermostat uses the batteries as a backup for the 24V power source. It is recommended to replace the batteries annually.

The steps you need to follow to replace the batteries of these models are as follows:

  • First, switch off the system.
  • Next, you need to draw out the cover plate of the Honeywell thermostat to separate it from the wall plate.
  • When you turn over the cover plate, there are two AAA batteries. Remove the old batteries and replace them with new ones.
  • Install the cover plate back onto the wall plate.
  • Switch the system on again.

Battery Replacement in Honeywell 3000 Series – TH3110D

The old Honeywell thermostat of 3000 series was TH3110D. Honeywell discontinued it on Jul 13, 2019. This PRO series provided non-programmable thermostats for 24 VAC conventional and heat pump systems or 750 mV heating systems.

It has easy-to-use slide switches that allow you to select the heat or cool mode, and operate the fan. If your 3000 series old Honeywell thermostat connects to AC power source, the batteries are completely for backup power.

The batteries provide power backup to the display in case of power interruption. The display flashes a “Replace Batt” sign when the thermostat runs out of batteries. It displays the battery replacement warning two months prior to battery depletion.

It is best to replace the thermostat batteries once a year or before leaving town for more than a month. Replace the batteries of your Honeywell thermostat 3000 series in following steps:

  • Pull at the bottom to remove the thermostat from the wall plate.
  • You will find 2 AA alkaline batteries when you turn over the thermostat.
  • Replace the old batteries with new ones.
  • Secure the thermostat back onto the wall plate.

Battery Replacement in the Honeywell 4000 Series – TH4110D and TH4210D

The Honeywell Thermostat 4000 Series includes the TH4110D and TH4210D models. These kinds of thermostats are programmable. Regardless of a heating pump, these models enable the heating or cooling systems to function.

Honeywell discontinued both the models in late 2018. They provided functional and Wi-Fi replacements for both models. The Honeywell Thermostat 4000 Series shows a warning sign of “Replace Battery” two months prior to the thermostat’s batteries running low.

The steps that you need to follow to replace the batteries of these models are as follows:

  • Switch off the system before replacing the batteries.
  • Tug the bottom of the cover plate to separate it from the wall plate.
  • When you turn over the cover plate, you’ll find two AA batteries. Replace them with new ones.
  • Secure the cover plate back onto the wall plate and switch on the system.

Battery Replacement in the Honeywell 5000 Series – TH5110D, TH5220D and TH5320U

There are three models of the Honeywell 5000 series or Focus Pro 5000 – the TH5110D, the TH5320U and the TH5220D. The TH5110D uses AAA alkaline batteries, while the other two models use AA alkaline batteries.

You will find the battery compartment at the side of the thermostat device. The steps that you need to follow to replace the batteries of these models are as follows:

  • Pressing the tab on the top side of the thermostat device to open the battery compartment. Tug out the compartment to separate it from the faceplate.
  • Replace the old batteries with the new ones.
  • Secure the battery compartment back into place. Gently push it to press it back into the faceplate.

Battery Replacement in Honeywell 6000 Series – TH6110D, TH6220D and TH6330U

The 6000 series is quite similar to the 5000 series in regard to battery replacement. The only difference in 6000 series is that it uses AA batteries.

The discontinued old models of Honeywell thermostats include TH6110D, TH6220D and TH6330U. TH6110D and TH6220D have been recently discontinued by Honeywell in Q2 of 2019, while TH6330U model was discontinued in Q1 of 2019.

Honeywell has also provided the users with functional and Wi-Fi replacements for the discontinued models. The steps of battery replacement in old Honeywell thermostats 6000 series are same as that of the 5000 series.

Battery Replacement in the Honeywell 8000 Series – TH8110U, TH8320U and TH8321U

The Honeywell 8000 series is one of the most multi-purpose thermostat devices out there. It has three models, namely the TH8110U, the TH8320U, and the TH8321U.

Honeywell discontinued TH8110U model on Jul 14, 2016. They discontinued the TH8320U model on Oct 10, 2015, while they discontinued TH8321U model on Apr 28, 2015.

These models have the ability to control two cooling and three heating systems, simultaneously. Their dehumidification feature works along with cooling and heating controls. The 8000 series has three AAA optional batteries.

They are only needed if the thermostat is directly connected to the AC power source. The steps to replace the batteries of these models are as follows:

  • First, you need to pull out the cover plate from the wall plate.
  • Turn over the cover plate to find the batteries. Replace the old batteries with new ones.
  • Secure the cover plate back onto the wall plate.

Summing Up

Honeywell thermostats show you a warning sign to replace the battery usually one or two months prior to the battery’s expiry. Refrain from using damaged or leaky battery because it might harm your thermostat device.

With these essential instructions to follow, you no longer have to scratch your head and wonder how to change the battery in the older models from Honeywell.

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