Do trane thermostats have batteries

T8400C, T8401C AND T8424C,D ELECTRONIC THERMOSTATS 68-0180-3 4 Location Install the thermostat about 5 ft (1.5m ) above the floor in an area with good air circulation at average temperature. See Fig. 3. Do not install the thermostat where it can be affected by: Š drafts or dead spots behind doors and in corners. Š hot or cold air from ducts.

View and Download Trane TCONT600AF11MA owner's manual online. Programmable Comfort Control. TCONT600AF11MA thermostat pdf manual download. ... • Make sure power switch at heating & cooling system is on. • Make sure furnace door is closed securely. • If thermostat is battery powered, make sure fresh AA alkaline batteries are correctly ...Before you begin, make sure the HVAC system is idle. You don't want to reset the system when it's running. Once idle, you can start to reset your Trane thermostat by following these instructions: In your circuit breaker, find the switch for your thermostat. Turn the switch off for about 30 seconds. Turn the switch back on.As a rule, thermostat batteries will need to change about once every year. If you periodically change them, you shouldn't have any problems maintaining control of your thermostat. In addition to a blank thermostat screen, other signs that you need to change your thermostat batteries include a lack of response in heating and cooling equipment ...How to Troubleshoot the Problem. Check Power Supply: Ensure the thermostat has power, whether from batteries or the HVAC system. Verify Settings: Confirm the thermostat is correctly set to cooling mode and the desired temperature. Inspect Wiring: Examine the thermostat's wiring connections for loose or damaged wires.After a power outage my XL824 thermostat does not remember the temperature that it was set on. Example, last night I touched the "sleep" preset, that is 69 degrees, when going to bed. We had about a two hour power outage and when the power came on the XL824 was set on 75 degrees. This is in the heat mode but the AC mode also changes.Trane XL824 Battery Replacement. You will have to change the batteries around once a year or more often depending on your battery quality. Dead batteries compromise the functionality of your thermostat since it powers all the electrical signals and actions of the thermostat. Also, they may be the reason why you are having a blank thermostat.Battery-powered thermostats are easy to install and can be used in any location. They are also useful in case of power outages, as they continue to work even …

I have a trane 5 wire thermostat. Can I connect a nest learning thermostat my wires are G O Y R. TH 6220D1051. I have - Answered by a verified HVAC Technician. ... If not, you will need a thermostat with batteries. Ask Your Own HVAC Question. Customer reply replied 4 months ago.To do this, touch the MULTIPLE DAYS button on the touchscreen. To set the first temperature program, touch the WAKE UP button on the touchscreen. Adjust the UP/ DOWN arrow keys displayed on the touchscreen to the time of day you want the wake-up temperature to start. Set the minimum and maximum temperature settings, using the other two sets of ...Trane® XR724 Fails to Enroll. Trane® XR724 Enrolled but not Connected to WiFi. How to Enroll a Trane® XR724 WiFi Thermostat. Reconfiguring WiFi for a Trane® XR724 Thermostat. How To Set Temperature High and Low Alerts (XL624 and XR724 Only) Knowledge base articles that apply only to the XR724 WiFi Thermostat.Sep 22, 2023 · Not all Lennox thermostats have batteries. This is dependent on the model and whether batteries are required for it to function properly. Most of them are connected to the building’s main power supply, but some need batteries to operate probably. You can check the model’s product description to know its power source. Select “Factory Reset” and then “OK.”. The thermostat will prompt you to confirm the factory reset. To continue, choose “Yes.”. Wait for at least 5 minutes and then configure your thermostat’s settings from scratch. Your “battery low” message will now be gone as you now, in fact, have a brand new thermostat.This video tutorial guides you through the process of changing the batteries in your Honeywell Thermostat. 🔧 Subscribe to our channel: https://www.youtube....

The answer is yes, most Lennox thermostats do have batteries. The batteries in a Lennox thermostat are typically used to power the display screen and other functions of the thermostat. The type and number of batteries required can vary depending on the model of the thermostat. Some Lennox thermostats may require AA or AAA batteries, while ...Without a C-wire, power does not continuously flow to Wi-Fi and smart thermostats. Some thermostats such as the Nest, have an inbuilt internal battery to bypass the need for a C-wire. That being said, for 10-15% of installations, a C-wire is still needed for the Nest. If your system doesn't have a c-wire, once can be added.Trane ComfortLink® II XL850 Thermostat. The Trane ComfortLink® II XL850 has all the same great features as the ComfortLink® XL1050, just with a slightly smaller screen. This thermostat’s touch screen size is 4.3″ with full color, so it’s still easy to read and program your thermostat. Enjoy impressive features like Wi-Fi and ethernet ...ComfortLink™ Trane XL850 Smart Control User Guide The XL850 is an easy-to-use, programmable control with a color touch-screen. When connected with Trane® Home you can control your home’s heating and cooling system and up to 230 separate Z-Wave™ devices from a smartphone, PC or tablet from virtually anywhere. This guide will help you

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If you are home during a power outage, taking the steps below can help prevent damage caused by spikes or flickering when power is restored.: Flip the breakers for your HVAC system and other major appliances to the OFF position. Turn off the power strips or unplug the power cables for your other electronic devices.Without a C-wire, power does not continuously flow to Wi-Fi and smart thermostats. Some thermostats such as the Nest, have an inbuilt internal battery to bypass the need for a C-wire. That being said, for 10-15% of installations, a C-wire is still needed for the Nest. If your system doesn't have a c-wire, once can be added.When you notice your battery is heating up, the first thing you should do is remove it from the device it's in. Do not try to handle or move the battery with bare hands or use it in any way. Keep it away from flammable materials as well. Once you have safely removed the battery, you need to dispose of it properly.1. Backup Power: One of the primary reasons thermostats have batteries is to provide a backup power source. In the event of a power outage, the batteries ensure that the thermostat continues to function and retain its programmed settings.Apr 16, 2022 · How to replace thermostat batteries Change Batteries in a Thermostat trane #Shorts #DIYMore Videos:https://www.youtube.com/channel/UCInBjHML3FhifZZuYcOFxSwCh...

Trane is one of the biggest names in the HVAC industry, and have been creating home comfort systems for more than 120 years. They are known for their innovative designs and excellent features. The Trane XL824 thermostat is probably the best value for money in the Trane range of smart thermostats – providing a good balance between …Trane smart thermostats will anticipate your temperature needs without you having to provide any input. The Smart Thermostat systems will monitor and adjust home temperatures independently. The Trane Smart Thermostat will learn your habits around the home and your time away. This information will be incorporated into the management of your HVAC ...The Trane XR400, XR300, XR200, XR100 Series thermostats have a 5-year limited warranty on functional parts. As part of our continuous product improvement, Trane reserves the right to change specifications and design without notice. Read important energy cost and efficiency information available from your dealer.3 Troubleshooting. Download this manual. Trane XL824. Connected Control. TCONT824 Installation Guide. ALL phases of this installation must comply with NATIONAL, STATE AND LOCAL CODES. IMPORTANT — This Document is customer property and is to remain with this unit. These instructions do not cover all variations in systems or provide for every ...The C wire, or "common wire" enables the continuous flow of 24 VAC power to the thermostat. Technically speaking, power flows from the R (red) wire, but not continuously (not on its own, anyway). To make it continuous requires a common wire to complete the circuit. When the circuit is complete, 24V energy will flow continuously.My Thermostat is Blank/Has a White or Black Screen. Enabling and Disabling Emergency Heat. Thermostat is Already in Use During Registration. Thermostat and Mobile App Display Different Temperatures. See all 7 articles. Knowledge base articles and troubleshooting assistance for WiFi thermostats including XL824, XL850, XL1050, XR724.A blank screen on a Trane thermostat is a common issue that occurs. Its causes can range from something easily fixable to an issue that requires an experienced technician to repair. You can do some troubleshooting to get to the heart of the problem. Remove your Trane thermostat from the wall and check the batteries if you see a blank screen on it.A C-wire, or a common wire, runs from your low-voltage heating system (24v) and carries continuous power to your thermostat. In today's electric market, most newer heating and cooling systems have C-wires, which guarantees compatibility for the installation of all smart thermostats. If you do not have a low-voltage heating system, you will ...Demonstrating how to use a Trane thermostat. In this video I go over how to set the air conditioner and the heater as well as adjustment of the temperature a...Thermostats will work without batteries if they are wired to your home’s grid. However, thermostats that contain a battery compartment won’t work if there are no batteries. You generally need to change your thermostat batteries every 10 months, but they can last up to 1 year. Smart thermostats often have internal batteries, but most of ...Programming a Trane thermostat begins with selecting the comfort control you want to set. Set the clock or day schedule, and press the up and down buttons to select the weekday sta...Five-minute time delay for compressor protection. Outdoor temperature display. Compatible with 3 wire zone valves, mili-volt and dual fuel systems. XR302. Control your home comfort with the Trane XR302 digital programmable thermostat that's compatible with up to three heating stages and two cooling stages.

Find information about Trane serial numbers at Trane.com. Click the Go to Trane Residential link under the Residential heading on the home page. Next, click the Warranty & Registra...

This exchange-traded fund is positioned to give investors exposure to companies taking meaningful steps toward reducing greenhouse gas emissions -- will it work and will it make yo...We looked at various models of the most commonly used 4-wire thermostat brands and labeled the following 5 as "the best:". Ecobee Lite Smart Thermostat. Honeywell Home CT410B Thermostat. Google Nest Smart Thermostat for Home. Honeywell Home RTH6360D1002 Programmable Thermostat. Honeywell Home 7-Day Programmable Touchscreen Thermostat, 1.The T terminal on old trane thermostat. The terminal was an outdoor compensation for heat anticipator in heat pump mode and usually it went to the thermostat. You wont need to wire this on a new programmable thermostat and you will have to tape it off. X2 Wire. The X2 wire on old trane thermostat was for emergency heat.To replace the batteries on the Sensi smart thermostat: Grab the face plate with both hands and pull straight towards you. After a tug, the face plate will detach from the sub-base. Remove the 2 AA Alkaline batteries from the face plate. Allow the front display to go blank. Insert 2 fresh AA Alkaline batteries, and push the face place back onto ...Flip up or pull off the thermostat housing (this is normally the hardest part). Locate the batteries. Take out the old batteries with your hand. If you need to use your flat-head screwdriver for assistance, be gentle. Put in the new batteries as marked. Flip shut or snap the thermostat housing back onto the wall plate.My Trane HVAC thermostat has gone blank. It doesn't use batteries. I've checked the HVAC unit and there's no standing - Answered by a verified HVAC Technician ... Okay let's make sure your thermostat does not have batteries. Pull the screen towards you, it will unclip from the wall plate. If it does not have batteries make sure the wire in C ...Yes, the ecobee thermostat has a battery power backup. This backup feature allows the thermostat to continue to operate even if your home loses power. The ecobee thermostat’s battery is a 3V CR2032 lithium coin cell battery. This battery should last about two years and can be easily replaced when needed.

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Posting Permissions. My Trane ComfortLink II XL1050 was set on Cool, 76 degrees and the power went off and was off for 3 hours. When the power came back on my ComfortLink went through a lengthy reboot (for lack of better term) and was showing a room temperature of 70 degrees. 70 degrees is far lower than the set point of 76 degrees for …If you have any questions or need assistance, please contact Trane Home Customer Support via email at [email protected] or call 1-877-288-7707, Monday-Friday 9 AM - 8 PM ET, and Saturday 10 AM - 5 PM ET. Trane® HVAC Systems and Thermostat Compatibility The compatibility matrices below are intended to help you identify which Trane smart...Problem 3: Your Sensi thermostat is not turning on the AC. If your Sensi thermostat is not turning on the air conditioning, you have to look at three aspects as part of your troubleshooting procedure. 1. Possible power outage in the neighborhood. First of all, ensure that there is no power outage in your neighborhood.Last, smart thermostats are becoming much more affordable. Google released a new Nest Thermostat model in 2020 that now costs $100, while smart home startup Wyze has a smart thermostat that costs ...These wall thermostats do not use power from the 24V thermostat wiring system and its low voltage transformer, and typically these thermostats will have larger batteries than those using battery power only for temporary backup. Question: where to put batteries in our Hunter 44422 Thermostat - Hunter Fan Company Programmable Thermostat InstructionsJust make sure to check the alignment of the battery terminals before putting new batteries in the thermostat. ... Recently I have noticed that my Trane Smart thermostat will be allowing the "temp reading" on its face to show a temperature several degrees higher than it is set for and the humidity has soared to a high 60-68. The thermostat ...My Thermostat is Blank/Has a White or Black Screen. Enabling and Disabling Emergency Heat. Thermostat is Already in Use During Registration. Thermostat and Mobile App Display Different Temperatures. See all 7 articles. Knowledge base articles and troubleshooting assistance for WiFi thermostats including XL824, XL850, XL1050, XR724.Just so, do all Trane thermostats have batteries? Not all thermostats use batteries; many are wired into the electrical system of the house. If you have a unit that uses battery power, remove the front plate from the wall plate and change the batteries to see if this brings the thermostat back to life again.There are several common reasons why your thermostat might not be getting enough power to work. The most common reasons include: A Tripped Circuit Breaker. Low Batteries. A Dirty Thermostat. A Bad Connection. A Blown Thermostat Fuse. A Bad Thermostat. Power Outages.Every thermostat needs a red wire to function because the red wire's main function is to provide 24-hour volt AC power from the transformer to the HVAC system, including the thermostat. Without a connected red wire the HVAC system cannot work. Thus, the red wire must be connected to your thermostat as it is literally the "lifeline" of ...When you notice your battery is heating up, the first thing you should do is remove it from the device it's in. Do not try to handle or move the battery with bare hands or use it in any way. Keep it away from flammable materials as well. Once you have safely removed the battery, you need to dispose of it properly.If your thermostat needs three wires it is most probably a digital thermostat connected to a boiler. There is a 24-volt hot wire, a 24-volt C wire, and a white wire. Battery-powered thermostat - four wires. This configuration is for a battery-powered thermostat but can also be for a digital thermostat that solely regulates heat. ….

TRANE COMFORT LINK II, THERMOSTAT IS BLANKED OUT, HAVE REMOVED IT FROM THE WALL AND WHERE THE BATTERIES WOULD SEEM TO BE, THERE ARE NONE. ANY IDEAS? Contractor's Assistant: Do you know the model of your Trane thermostat? How old is it? TCONT900AC43UA. Contractor's Assistant: How long has this been going on with your Trane thermostat? What have ...XR401 Comfort Control's memory eliminating the need for battery backup in the event of power loss. Simply follow the steps in this instruction manual and begin enjoying the benefits of your new Trane XR401 Comfort Control. Pub. No. 22-5206-01 Warranty Limited Warranty Low Voltage Comfort ControlTrane’s large, user-friendly touchscreens make it easier than ever to program an energy-saving schedule every day of the week. With optional Trane Diagnostics, your smart thermostat can even monitor your system in real time and alert your Trane dealer if there is a problem. Some smart thermostats feature a Bridge for Z-Wave® devices.The specific gravity of a battery should be between 1.265 and 1.299 for lead-acid batteries. This range indicates that the battery is fully charged and in good condition. If the specific gravity is below 1.225, the battery is discharged and needs to be charged. If the specific gravity is above 1.299, the battery is overcharged and may be damaged.I have a trane 5 wire thermostat. Can I connect a nest learning thermostat my wires are G O Y R. TH 6220D1051. I have - Answered by a verified HVAC Technician. ... If not, you will need a thermostat with batteries. Ask Your Own HVAC Question. Customer reply replied 4 months ago.Generation 3: Trane® XL824 & XL850 thermostats. Generation 5: Trane XL1050 thermostats, and newer XL824 & XL850 thermostats. Generation 6: Standalone bridge, white casing with Nexia logo NOTE: If you are unsure whether your XL824 or XL850 thermostat is Generation 3 or 5, please contact Trane Customer Support for assistance.Thermostat Loses WiFi Connection Often Most computers do not stay connected to a wireless network as long as a thermostat does. It is not uncommon for a thermostat to temporarily lose its connection with a wireless network from time to time. Like most WiFi-enabled devices, the thermostat is designed to automatically reconnect to the network.Trane touchscreen thermostat TCONT302 and TCONT303 guide. Guide for the remote space sensor and osa sensor WARNING: Information in this article is intended for use by individuals possessing adequate backgrounds of electrical and mechanical experience and who comply with all federal, state, and local laws, rules, orders, or regulations related to the installation, service, or repair of a ...Even though your AC unit is connected to your home's electrical system, it needs a stronger boost to work effectively. That's because air conditioners are high-powered machines that require a lot of energy to do what they're built to do, and your home's wiring simply doesn't provide the adequate amount of power to get the job done. The capacitor compensates by kickstarting your ...Check out the Trane owner's guides for more information about your air conditioner, furnace, heat pump or other Trane HVAC product. We use cookies to enhance your experience on our website. ... Trane Touchscreen Thermostat TCONT 302 and 303 Models: TCONT302, TCONT 303. Download manual. XR203 Programmable Thermostat Model: TCONT203AS42MA. Do trane thermostats have batteries, Trane’s XR203 Thermostat. One traditional thermostat is the Trane XR203. It’s digital, but it doesn’t have Wi-Fi capability. For homeowners who want as few bells and whistles as possible, this is a wise choice. Though it doesn’t have the features of Trane’s “smart” thermostats, it is still programmable., How to replace thermostat batteries Change Batteries in a Thermostat trane #Shorts #DIYMore Videos:https://www.youtube.com/channel/UCInBjHML3FhifZZuYcOFxSwCh..., Jul 20, 2021 ... ... I'm going to use instead. 00:00 Intro 03:27 Temperature Goes Wild 07:33 WiFi Doesn't Reconnect 10:52 Nexia App Issues 12:32 What Will I Do?, A blank screen on a Trane thermostat is a common issue that occurs. Its causes can range from something easily fixable to an issue that requires an experienced technician to repair. You can do some troubleshooting to get to the heart of the problem. Remove your Trane thermostat from the wall and check the batteries if you see a blank …, Wireless Thermostat Will Not Connect to WiFi (Red X over Green Bars) Wireless Thermostat Connected to WiFi (Green Bars) and Disconnected From Trane® Home Network. Screen is Out of Calibration/Buttons Don't Activate When I Press Them. Thermostat is Disconnected - Trane® XL824/850/1050. How To Enroll Trane® XL824/824B, XL850, and XL1050 ..., Trane XL824 Smart Control User Guide The XL824 is an easy-to-use, programmable control with a color touch-screen. When connected with Nexia™ Home Intelligence, you can control your home's heating and cooling system and up to 230 separate Z-Wave devices from a smart phone, PC or tablet from virtually anywhere. This guide will help you, Battery Replacement. Stage Cooling with GAT2, GAM2 & TEM3. Wiring Diagrams. Or 2 Stage Heat Pump with TAM7/TAM9 (24V Mode) ... Trane XR203 Programmable Thermostat Heat Pump Package Unit with Non Variable Speed Blower Thermostat Indoor Unit W2/X2 NOTES: 1) Wire third party condensate over ow switches between Y of the thermostat and Y1 of the air ..., In most situations, you will notice that the thermostat will contain AA, AAA, 3V lithium-style batteries, or alkaline batteries. Some thermostats use a 9V battery. Suppose the battery capacity is very low, then the display will indicate a low battery, which means it is time to change the battery for your thermostat to make it function efficiently., 1. Precision Temperature Control. One of the key ways smart thermostats save money is through precision temperature control. Traditional thermostats rely on manual adjustments, often leading to temperature overshooting and wasting energy. Smart thermostats, on the other hand, can maintain a more consistent temperature by learning …, attery powered (1 year battery life)B. . ush notifications when battery is low through kumo cloud appP. WIRELESS TEMPERATURE AND HUMIDITY SENSOR FOR kumo cloud. SPECIFICATIONS. . xtends CN105 connection an additional 50 feetE. . or use with kumo station, Wireless Interface 2, and USNAP InterfaceF. IT EXTENDER. PAC-WHS01IE-E PAC-USWHS003-TH-1 ..., Most digital thermostats are both hardwired to your house and have backup batteries. The reason for having backup batteries is to save any programmed information. Knowing what to expect when batteries are low or changing them annually can help you take care of your HVAC system. Knowing whether or not your thermostat has batteries or not could ..., The Trane XT500C deluxe programmable heat pump thermostat thermostat can be used to manage the temperature of the rooms where it is installed. This owner's guide contains the 68 pages of information you need to get started with the device and configure for different applications based on needs correctly. Owners guide for Trane XT500C deluxe ..., Contractor's Assistant: How long has this been going on with your Trane thermostat? What have you tried so far? I have taken apart the t-stat, cleaned the battery terminals, cleaned the corrosion from the PC board, put in new batteries, and replaced the backup battery. Corrosion to the PC board looks non-reversible., Posting Permissions. Hello all - I've learned a ton reading this forum, thanks for all the help that has been handed out. Back in February I replaced a 20 year old Lennox system and purchased a 3 ton Trane 2 stage condensor (XR17), variable gas furnace/blower (XV80), and a thermostat (TCONT824). I didn't go cheap, went with a reputable dealer ..., Many thermostats still use batteries, while others draw power from your home's electrical or HVAC system. The typical battery-powered dial, switch, digital or ..., Description. Controlling the climate in your home is not an easy task and the Trane XL824 thermostat will do just that. To ensure proper operation of the Wi-Fi smart thermostat, study user guide, presented in a convenient graphical format that contains 20 pages with useful information. User guide for Trane XL824 Wi-Fi smart thermostat on 20 pages., Link Thermostat (UX360) - Trane Home. Trane Home. Link Systems. Link Thermostat (UX360), Trane XL824 Outdoor Temp Sensor. I had an all new system installed with a Trane XL824 thermostat. Everything works great. However the outdoor temperature sensor on the thermostat either by local Nexia weather or the remote sensor is out of calibration by Atleast 8-10 degrees. -Nexia internet weather says 40 degrees. -Weather.com says 31 degrees., 3 Troubleshooting. Download this manual. Trane XL824. Connected Control. TCONT824 Installation Guide. ALL phases of this installation must comply with NATIONAL, STATE AND LOCAL CODES. IMPORTANT — This Document is customer property and is to remain with this unit. These instructions do not cover all variations in systems or provide for every ..., Trane’s large, user-friendly touchscreens make it easier than ever to program an energy-saving schedule every day of the week. With optional Trane Diagnostics, your smart thermostat can even monitor your system in real time and alert your Trane dealer if there is a problem. Some smart thermostats feature a Bridge for Z-Wave® devices., Join SS&B Heating & Cooling as we walk you through the setup process for your Trane XR402 thermostat. In this informative and easy-to-follow video, provides ..., 1. Precision Temperature Control. One of the key ways smart thermostats save money is through precision temperature control. Traditional thermostats rely on manual adjustments, often leading to temperature overshooting and wasting energy. Smart thermostats, on the other hand, can maintain a more consistent temperature by learning from occupants ..., A low battery on the thermostat can affect how your thermostat operates. However, this can depend on the type of thermostat you have. A low battery may not affect how it works if you have a digital thermostat with a c-wire connection. But if you have a thermostat without a c-wire connection, a low battery will probably affect how it works., Most thermostats can last 10 years. After 10 years, they can show signs of age and wear, which means it's time to replace it. Common problems with bad thermostats include faulty sensors, digital screens, etc. If the thermostat goes bad, it can cause your HVAC system to run continuously or not run at all., Thermostats will work without batteries if they are wired to your home’s grid. However, thermostats that contain a battery compartment won’t work if there are no batteries. You generally need to change your thermostat batteries every 10 months, but they can last up to 1 year. Smart thermostats often have internal batteries, but most of ..., Looking to replace your batteries on your 800 series Trane thermostat? Simply pull the thermostat straight out and you'll see the AAA batteries located on t..., BNGS comfort consultant demonstrates changing the batteries on a touchscreen thermostat, How to Troubleshoot the Problem. Check Power Supply: Ensure the thermostat has power, whether from batteries or the HVAC system. Verify Settings: Confirm the thermostat is correctly set to cooling mode and the desired temperature. Inspect Wiring: Examine the thermostat’s wiring connections for loose or damaged wires., Thermostats. Adjust how your home feels with thermostats that communicate directly with your system. Connect to WiFi to manage your comfort preferences. Choose how your system heats and cools your space with simple controls. Divide your home into climate zones and control each room's temperature with your thermostat., Lowering the temperature of your thermostat can do more than reduce your energy bill (although we think that benefit is so awesome that it still made the list). Dropping temps just..., Follow all of the prompts and press Apply when it appears on the screen. The thermostat will apply the changes and return to the Custom Schedules screen after a few moments. You can manually customize schedules using the buttons on the Custom Schedules screen. Select Grouping. Select the days of the week that will follow the same schedule., , If it's a battery operated thermostat, toggling the fan switch will allow the fan to operate despite the battery condition. As PJmax suggested, the furnace (or A/C) will NOT operate if the batteries are weak or dead. These thermostats utilize the battery power to actuate a relay in the 'stat to turn on the furnace or A/C.