Remove the thermostat from the wall and locate the battery compartment
Most Honeywell thermostats run on two AA or AAA batteries, and you can change them without calling a technician. The first step is to remove the thermostat from its wall mounting. Look for a slot or tab on the bottom or side of the unit—push or slide it gently to release the thermostat from the base plate that stays mounted on the wall. Set the thermostat face-down on a clean, flat surface so you can see the back.
The battery compartment is usually on the back of the unit, marked with a small door or cover. You may see a diagram printed on the back showing which way the batteries go (+ and − symbols). If your model has a battery cover, slide or unclip it to open the compartment. Some Honeywell models have the batteries visible without a cover—you'll see them sitting in a plastic holder with metal contacts on each end.
Key Takeaways
- Remove the thermostat from the wall by pushing the release tab or slot on the bottom or side, then set it face-down on a clean surface.
- Most Honeywell thermostats use two AA or AAA batteries; check the back of the unit or your manual to confirm the size.
- Replace both batteries at the same time, even if only one is dead, and match the + and − ends to the diagram printed on the compartment.
- After inserting new batteries, reattach the thermostat to the wall base and check that the display lights up and shows the correct time.
Remove the old batteries and note their orientation
Gently pull or slide the old batteries out of the compartment. They may be held loosely or seated firmly—use steady pressure rather than force. As you remove them, notice which end (+ or −) was pointing toward which contact. Most battery holders have a small spring or metal tab at one end and a flat contact at the other; the spring end usually holds the + (positive) end of the battery.
If the batteries are stuck, do not pry them with a metal tool—you risk damaging the contacts. Instead, try rocking the battery gently side to side while pulling, or use a plastic spoon handle to nudge it out. Once both are out, set them aside. If they are old or corroded, dispose of them at a battery recycling center or electronics store rather than in the trash.
Insert new batteries in the correct direction
Take two fresh AA or AAA batteries (whichever size your model requires) and check the diagram on the back of the thermostat or inside the battery compartment. The diagram will show which end goes in first. Typically, the + end goes toward the spring contact and the − end goes toward the flat contact, but always follow the diagram for your specific model.
Slide or insert the first battery with the correct end leading. You should feel it seat into place. Insert the second battery the same way. Both batteries should sit flat and flush in the compartment—if one is sticking up or feels loose, remove it and reinsert it. Do not force them; they should slide in smoothly. Once both are in place, close the battery cover or door if your model has one.
Reattach the thermostat to the wall base
Pick up the thermostat and align it with the base plate on the wall. The mounting slots or tabs on the back of the thermostat should line up with the base. Slide the thermostat upward or push it straight in—the exact motion depends on your model, but you should hear or feel a click when it locks into place. The thermostat should sit flush against the wall with no gaps.
Check that the display lights up and shows the current time and temperature. If the display is blank or shows a low-battery symbol, remove the thermostat again and double-check that both batteries are seated correctly and facing the right direction. A common mistake is inserting one battery backward; even one reversed battery will prevent the thermostat from powering on.
Verify the thermostat is working and set the time if needed
Once the display is on, look at the screen to confirm it shows the correct time. If the time is wrong, you may need to reset it. Most Honeywell thermostats have a small button labeled "Time" or a menu button on the front—press and hold it until the time display begins to blink, then use the up or down arrows to set the correct hour and minute. Consult your manual if you are unsure which buttons to use, as the process varies by model.
Test the thermostat by adjusting the temperature up or down a few degrees. You should hear the heating or cooling system respond within a minute or two. If nothing happens, check that the thermostat is set to "Heat" or "Cool" mode (not "Off") and that the system switch at your furnace or air handler is turned on. If the display still does not respond, remove the thermostat again and verify once more that both batteries are fresh, the correct size, and inserted in the right direction.
Common mistakes to avoid when changing batteries
The most frequent error is inserting one battery backward. Even if the battery compartment is loose enough to allow it, a reversed battery will break the circuit and the thermostat will not power on. Always check the diagram before inserting and double-check after closing the cover. Another common mistake is using old or partially dead batteries. If you have any doubt about the age or condition of the batteries, use new ones from a fresh package.
Do not mix battery types—use two AA batteries or two AAA batteries, not one of each. Do not leave the thermostat off the wall for more than a few minutes during the swap, because some models will lose their programming if power is interrupted for too long. If you do lose your settings, you will need to reprogram the thermostat with your preferred temperature schedule. Finally, do not use rechargeable batteries unless your manual specifically says they are safe; most Honeywell thermostats are designed for alkaline batteries.
When to replace batteries and what to expect
Honeywell thermostat batteries typically last one to two years, depending on the model and how often the thermostat adjusts the heating or cooling system. You will see a low-battery warning on the display—usually a small battery icon or the words "Low Batt"—several weeks before the batteries are completely dead. This warning gives you time to purchase new batteries and change them before the thermostat loses power.
If you change the batteries before the warning appears, you are replacing them early, which is fine and does no harm. If you wait until the display goes blank, the thermostat will lose its time and any custom schedule you have set, and you will need to reprogram it after installing new batteries. For this reason, it is a good idea to change batteries as soon as you see the low-battery warning rather than waiting until the unit stops working.
Frequently Asked Questions
Can I change the batteries while the thermostat is still on the wall?
No. You must remove the thermostat from the wall base to access the battery compartment on the back. The process takes only a minute or two, and removing it ensures you can see the batteries clearly and insert them correctly without fumbling.
What size batteries does my Honeywell thermostat use?
Most Honeywell thermostats use two AA batteries, but some models use AAA. Check the back of your thermostat or the battery compartment itself—the size will be printed there. You can also check your manual or the model number on the thermostat's label, which you can search online to find the specifications.
What happens if I put the batteries in backward?
The thermostat will not power on. The display will remain blank because the circuit is broken. Remove the thermostat, take out the batteries, and reinsert them with the + end toward the spring contact and the − end toward the flat contact, following the diagram on the back.
Do I need to reprogram the thermostat after changing the batteries?
If you change the batteries before the display goes blank, the thermostat will keep its time and schedule. If the display was already off when you changed the batteries, you will lose the time and any custom temperature schedule, and you will need to reprogram them after the new batteries are installed.
Can I use rechargeable batteries in my Honeywell thermostat?
Most Honeywell thermostats are designed for alkaline batteries and may not work reliably with rechargeable ones. Check your manual to confirm whether rechargeable batteries are safe for your model. If your manual does not mention them, use alkaline batteries to avoid problems.