Complete Guide to Heating, Heat Pump, or Air Conditioning Thermostats

How to buy, install, wire, use, adjust, or repair room thermostats

Air Conditioning, Cooling-Only Thermostats

Where can I buy a two-wire thermostat (red & white) will work for my A/C system?

I have just an air conditioner unit and trying to find just a thermostat just for a/c (no heat).

I have tried to use the ones for heat and air and they wont work.

I've just got two wires white and red one, please help - On 2011-05-25 by lisa

by (mod) -

Lisa

You're right that a "heat only" thermostat is going to try to turn heat ON when the temperature DROPS below the set point on the thermostat, while what you want is a thermostat that turns your air conditioner ON when the temperature RISES above the thermostat set point.

So if your system uses a two-wire (red and white) thermostat, just about any 14-V two-wire air conditioning-only thermostat you'd find at a building supplier would work.

The "trick" here is that when shopping for a thermostat you need to ask for a "cooling only" or an "air conditioning" thermostat, and you also need to specify which of two types you need:

1. A low-voltage (24VAC) thermostat for cooling-only (that sounds like what you want as you say you've just got small-diameter red and white thermostat wires to hook-up)
   
   Above I show a "cooling only" or "air conditioning" low voltage (24VAC) thermostat produced by White Rdogers, their Mechanical Cool Only Thermostat, 0 H, 1 C, Hardwired, 24VAC Mfr # 01C21 101S1 as sold at zoro.com for less than $20. U.S.
   
   Watch out: for you it sounds like this is correct, UNLESS your system requires a line voltage (120V or 204-volt) thermostat and wiring.
2. A line voltage thermostat (120VAC or 240VAC) for cooling-only application.

Below I show an example of a line voltage cooling-only thermostat from King Electric, their Single Pole Cooling Non-Programmable Thermostat 120/208/240-22 Amp and 277-Volt-18 Amp in White, that sells (at Home Depot or similar suppliers) for under $80. U.S.

Watch out: when working on a line voltage thermostat (which should NOT be your case), with power on there are shock and electrocution hazards - hire a qualified service tech.

Check the voltage at the wires if you are qualified to do so safely, or look at your A/C unit or heating and cooling system to see if you can trace your thermostat wires back to a low-voltage thermostat transformer. That will tell you what type of equipment you have.

Antique, Traditional & Early Clock Thermostats & How They are Set

The round Honeywell® wall thermostat shown in the photo above has been locked in a plastic enclosure to prevent people from changing its set temperature.

Set temperature and how the thermostat works are described in excruciating detail below for each of the different types of room thermostats.

At HEAT ANTICIPATOR ADJUSTMENT we describe how an internal adjustment can be made to this thermostat to improve its operation in some types of heating systems.

Also see THERMOSTAT CALIBRATION where we discuss the accuracy and calibration of room thermostats.

Historic GE Technotron & Honeywell Chronotherm Thermostats

Our photo illustrates General Electric's Telechron thermal control (room thermostat) first produced in 1933.

This was probably the first clock-controlled automatic set-back residential wall thermostat produced in the U.S. The top of the thermostat is hinged to permit acces to its interior for wiring.

GE Telechron Thermal Control (thermostat) is described by the U.S. Smithsonian Institute's National Museum of American History:

General Electric manufactured this Thermal Control thermostat around 1933. The thermostat came equipped with a Telechron synchronous motor that powered the clock attached to the thermostat.

The clock allowed the furnace to turn on and off at a certain time, and the thermostat has two wheels on the right and the left, which allowed the home owner to set a desired temperature during the day and during the evening. - retrieved 2017/12/31,

- original source: Smithsonian Institute, National Museum of American History, Constitution Avenue, NW Between 12th and 14th Streets Washington, D.C., USA, americanhistory.si.edu/collections/search/object/nmah_1392737

Below is a later clock-thermostat more-widely sold in the U.S, the Honeywell Chronotherm wall thermostat, another clock-operated automatic day-night room thermostat.

The Honeywell Chronotherm thermostat is described in

this 1950's HONEYWELL THERMOSTAT GUIDE [PDF]

produced by the Minneapolis-Honeywell Regulator Company, Minneapolis 8, Minnesota, (1950) reproduced from a Dodge building products catalog.

Clicking on the first page in that PDF file should return to this web article.

Excerpts from the original Honeywell Chronotherm product literature:

The Chronotherm is an electric clock thermostat which automatically matches the room temperature to your living schedule. All day long it controls the burner to maintain the exact temperature you want.

A special "Comfort" feature in the instrument assures extremely accurate control. It senses heat requirements quickly. There is no under-heating to cause chills, no overheating to waste fuel.

At bedtime, this never-forgetting instrument lowers the room temperature as you wish for your sleeping comfort. ... it saes up to 20% of yoru costly fuel.

Then in the morning the Chronotherm automaticallyi raises the room temperature to the daytime cofort level. ...

If you plan to leave over a week-end, it's a simple matter to save fuel while you are gone.

The handy finger-tip levers on the Chronotherm allow you to lower the temperature settings as you wish. - 1950's HONEYWELL THERMOSTAT GUIDE

Two other Honeywell thermostats sold in 1950 were the Time-O-Stat for semi-automatic day-night temperature control, and the Acratherm thermostat. We illustrate both of these below.

Room thermostats for air conditioning work and are set the same as when these devices are used for controlling heating systems. We provide lots of detail about how these devices work -

see THERMOSTAT SETTING INSTRUCTIONS.

Antique European Wall Thermostats

Question: Antique BR heating thermostat in Austria: Identify the brand?

[Click to enlarge any image]

I tried to search the brand of my thermostat without luck. Do you have any idea what year it could be from? It looks like it uses a magnet at the end of the coil – I don’t see any mercury. - Anonymous by private email 2023/09/24

Moderator reply:

That looks like a bimetallic spring and mercury bulb thermostat but I agree that instead of a classic glass bulb containing a visible drop of mercury the switch at the top of your thermostat is rectangular and not of glass, so we can't see its contents.

Significant, however is the BR logo on your thermostat. Notice that it's enclosed in a circle with wires that surround the letters B & R and between them is a classic image of a mercury bulb switch.

I showed these photos to BR Enclosures, an Australian company who in turn suggested that you try finding information from B&R Automation in Austria.

I haven't found the contact information for B&R in Austria. B&R Automation headquarters is in Roswell, Georgia in the U.S. This B&R company is currently offering roboics, automation, and supporting software.

• B&R Industrial Automation Corp. Suite 100 1250 Northmeadow Parkway 30076 Roswell, GA United States Phone : +1 770 772 0400 E-Mail : office.us@br-automation.com

I have posted your photos here to invite comments from our European and Asian readers and we'll add what we can find by further research.

When I asked BR Enclosures, an Australian company who manufaccture enclosures, if this is a brand that they know, BR Enclosures replied in minutes with their helpful suggestion.

Contact: enquiries@brenclosures.com.au Tel: +61 7 3714 1111 Website: https://www.brenclosures.com.au/

There is also a BR Bringer company in Germany who produce modern WiFi thermostats - a reasonable line of inquiry, sold on Amazon, but I was unable to find company contact information for that vendor.

Traditional Rectangular Wall Thermostats and how they are set

On this wall thermostat the red pointer shows the current room temperature.

The black pointer at the center of the scale at the bottom of the little window shows the temperature that the thermostat has been "set" to.

The "Set Temperature" is the temperature that the room occupant is requesting.

Moving the thermostat adjustment lever (located at the top, side, or bottom of the thermostat depending on the model) will change the set temperature up or down, causing the heating or air conditioning system to turn on or off as needed.

SeeTHERMOSTAT SETTING INSTRUCTIONS.

Traditional Round Room Thermostats

Traditional round wall thermostats like the Honeywell T87 shown above were first produced by Honeywell in 1953 and continue to the present day. Wikipedia and other sources note that the idea for for this round thermostat originated with Karl Kronmiller, a Honeywell engineer and its design was detailed by Henry Dreyfuss.

In its most-simple installation just two thermostat wires are used to operate a heating system and are connected Red to R and White to W on the thermostat.

Wiring and setting instructions for the traditional round thermostat such as the Honeywell T87 shown above are found at

• HEAT ANTICIPATOR ADJUSTMENT - T87
• ROUND WALL THERMOSTATS & how they are set
• THREE-WIRE HONEYWELL T87F TYPE THERMOSTAT WIRING

Programmable, Digital Room Thermostats & How They are Set

Digital room thermostats are illustrated in our two photographs shown here. A modern digital thermostat uses an LCD type display to show the current room temperature along with other information.

Typically the display changes in response to pushing the thermostat control buttons.

Most digital room thermostats are "programmable" - you can set the thermostat to set back the room temperature at night (in heating mode, for example) and many models allow different time and temperature settings both throughout the day and for individual days of the week as well.

Our digital thermostat shown at left indicates the time (5:43 PM) in the left side of the display and the current temperature (53 °F) in the right side of the display.

With the thermostat's plastic cover "shut" it's operation is very simple, just showing up and down arrows that temporarily call for a higher or lower room "set" or "desired" temperature.

We opened the plastic thermostat cover to show additional detailed controls and instructions.

Our Favorite Room Thermostat - The Honeywell RTH2300 / RTH221

The Honeywell RTH2300 / RTH221 series room thermostats are easy to program, permit different weekday and weekend programs, and include a "hold" button that is invaluable for keeping the thermostat at a fixed setting without losing the whole program.

Honeywell displays a "Rated Overall Best Brand" sticker on the packaging indicating that this model received a "Best" rating by an independent Frost & Sullivan study.

At THERMOSTAT SWITCHES, INTERNAL we describe how to set this thermostat's internal "Gas" or "Oil" slide switch.

At TROUBLESHOOT ACCURACY & RESPONSE of THERMOSTATS we describe the accuracy of this thermostat, typically +/- 1° F.

We describe the operation of a typical digital room thermostat for heating or air conditioning later in this article at DIGITAL ROOM THERMOSTAT OPERATION

A simpler programmable Honeywell® digital room thermostat is show in our photo at left. This is a Honeywell CT2700 Electronic Round Programmable Thermostat.

The thermostat is showing the current time (12:15 PM) and current room temperature (67 °F).

This unit does not provide additional buttons under a cover. But by pressing the center "Set" button the display changes to allow the user to set a desired time and temperature setting for day and night time temperatures.

At THERMOSTAT SWITCHES, INTERNAL we discuss setting the thermostat's internal F/E toggle switch.

Watch out: we installed and tested two of these thermostats over several years of use. While the device is simple, un intimidating, and easy to program, the lack of a "hold" feature was annoying and required more fooling around; we also would have liked an additional daytime automatic setback period that this device doesn't offer.

But the worst discovery was that our oil burner was short cycling, sometimes turning on for just a few seconds - a problem that we finally traced to a defect in one of these thermostats.

(The problem ceased when we swapped in our preferred thermostat shown above). We also found the flat cable wiring of this thermostat very fragile - eventually the display cable simply detached itself from its contacts.)

See also

• THERMOSTAT SETTING INSTRUCTIONS - How to Set the Thermostat
• DIGITAL THERMOSTAT OPERATION - how digital thermostats & their displays work
• THERMOSTAT SETBACK ADVICE

Nest™ Learning Thermostat

Home automation features include buiding occupancy monitoring & communicating with the Nest Protect Carbon Monoxide & Smoke Detector

"The Nest Learning Thermostat" is an electronic device that can control room temperatures and possibly other components connected to or installed as part of a home automation system. We have installed three of these in our test building and will report further on ease of installation, programming, and use as well as using and adjusting the Nest thermostat remotely from your cellphone, computer, or tablet.

Photo: the Nest® Learning Thermostat on demonstration display at a Home Depot store in 2013. [Click to enlarge any image]

Nest Learning Thermostat Installation & Use Article Series

• NEST LEARNING THERMOSTATS - home
  • HUMIDITY RESPONSE, NEST THERMOSTATS
  • NEST THERMOSTAT INSTALLATION & WIRING
  • NEST THERMOSTAT SET-UP & PROGRAMMING
  • NEST THERMOSTAT SET-UP COOL vs HEAT
  • NEST 2 vs NEST 3 THERMOSTATS
  • NEST THERMOSTAT WIRING INSTRUCTIONS for use with their Energy Kinetics 2000 MANAGER [PDF]

Backup Batteries & Default Programs for Digital Room Thermostats: blank thermostat display problems

Some programmable digital room thermostats include an internal battery that will allow the device to remember the program that you have set even if there has been a power outage. This topic has been moved to its own article

at THERMOSTAT BACKUP BATTERIES - for temporary or full time operation.

Digital Thermostat Display is Blank

I was changing the filter on my Trane air handler and when I put the blower door back on the thermostat was blank.

The thermostat doesn't require batteries and I made sure the circuit breaker is on. What else could it be? Thanks On 2018-06-29 by Anonymous -

by (mod) -

The most likely explanation is that your thermostat is taking power from a low voltage transformer on a circuit supplying power to the air handler and that would be left open or off if a blower door safety switch is not securely made when you put the blower door back on.

Check that first.

A digital thermostat that doesn't include a backup battery will go "blank" if the low voltage (24VAC) wires to the thermostat are disconnected or if power is off to the low voltage transformer supplying bvoltage to the thermostat.

I've also found that if there are too many thermostats and devices all being supplied by the orignal low voltage 24VAC transformer at your heater or air conditioner you may need to provide direct power to your thermostat.

We show how to do this at

ADD a COMMON WIRE at THERMOSTATS 

Radiator Thermostats & Baseboard Thermostats, Automatic - TRVs & How They are Set

Several manufacturers provide thermostatically-controlled radiator valves (Armstrong, Danfoss, Hoffman Specialty, Jacobus (Maid'O'Mist) and others).

Automatic radiator/baseboard valves provide thermostatic controls that can be installed on individual hot water radiators, steam radiators, or heating baseboards. The automatic radiator or baseboard valve will automagically open or close to attempt to control room temperature to the desired level.

Shown at left is an adjustable individual thermostatic control installed on a hot water radiator in Molde, Norway.

For details see RADIATOR VALVES & HEAT CONTROLS This article describes these automatic or thermostatically controlled radiator valves (such as the Armstrong RV-4) that will allow you to set the desired room temperature.

Also see RADIATOR STEAM VENTS, 1-PIPE SYSTEMS for a description of automatic steam vents used to control the rate at which steam heat radiators will get hot. Automatic steam vents can help balance the delivery of otherwise uneven steam heat throughout a building.

Remote Control Room Thermostats for Heating and Air Conditioning & How to Use Them

Remote control thermostats such as the unit shown at left are usually used with air conditioning or heating split systems using an outside compressor/condenser unit and one or more indoor wall-mounted cooling or heating units..

The thermostat controls in the hand-held remote control communicates with a wall-mounted air conditioner or heater using infra red signals.

The open finned area at the bottom of this Sanyo control (at the left in our photo) permits ambient air to enter the control for purpose of sensing the air temperature.

A control such as this Sanyo™ unit can be quite sophisticated and include automatic set back temperatures, timers, etc.

See SPLIT SYSTEM AIR CONDITIONERS & HEAT PUMPS for details, including troubleshooting and fixing remote control thermostats themselves

If you are looking for wireless thermostats see

WIRELESS & REMOTE THERMOSTAT CONTROLS for HVAC

Hand held A/C remote control does not seem to be working

Have a hand held remote for TCL air-conditioner (split model TAC-30CHS/G). when we set temperature, conditioner blinks what you want it to be, then it goes to inside temperature (suppose to do this) but then it quickly jumps to 34 degrees & switches off. Guessing it is thermostat? Anne Webber 9/2/11

Reply:

Anne, sounds odd to me too. Try

• putting a new battery in the hand held remote and reinitializing it
• turn off all system power when you're not already in the middle of a cooling cycle and leave it off for a minute - or if you were in cooling cycle, wait an hour, then turn power back on - resetting everything.
• be sure you've got clear line of sight between the remote A/C controller and the receiving unit
• be sure that the wall mounted thermostat (if there is a separate one) is properly located where it can see or communicate with the indoor wall mounted blower assembly.

If those steps don't fix the problem and you don't see more help in the installation and use manual, it's time to ask for an HVACR service call as there could be a bad controller, thermostat, or control board.

Outdoor Thermostats on the Heat Pump Compressor-Condenser Unit

Heat Pump Outdoor Thermostats are used to control the turning on and off of backup heat.

Our photo (left, courtesy of Neal Renn shows the thermostatic control unit in the outdoor compressor/condenser unit of a residential heat pump.

See HEAT PUMP THERMOSTAT, OUTDOOR

and BACKUP HEAT for HEAT PUMPS

Also see Detailed Case of

a Heat Pump that Put out Heat when Cooling was Required

Room Thermostat Temperature Sensor Types & Mechanisms

Our photograph illutrates a traditional bimetallic spring used in many thermostat interiors to sense and respond to room temperature.

A variety of methods are used to sense room temperature and to communicate that data to the thermostat's heating or cooling switching mechanism:

Air conditioning or cooling-only thermostats

While most room thermostats are designed to control heating and air conditioning or heat-only systems, for thermostats to be used to control air conditioning or "cooling-only" systems, models are sold that respond just to a temperature rise, turning on an air conditoning or cooling systems.

Details are at COOLING-ONLY THERMOSTATS

Bimetallic Element thermostats

 use a bimetallic spring consisting of strips of two different metals fused together, typically into a coil shape. As room air temperature causes the two metals to expand or contract at different rates, the effect is that the spring coils up or un-coils, moving a switch that turns heating or cooling or or off.

Bellows Element thermostats

are filled with a volatile liquid that vaporizes at temperatures typically found indoors. As the liquid vaporizes pressure inside the bellows expands, translating temperature change into the movement of a contact to turn heating or cooling on or off in response to building temperature.

Thermistor-type thermostats 

use a tiny solid-state electronic component, a type of resistor whose electrical resistance changes in response to temperature. By combining the thermistor with appropriate additional circuits and controls the thermostat uses the change in resistance to control the switching of the thermostat's control of cooling or heating on or off in response to room temperature.

For details: at TEMPERATURE RESPONSE of ROOM THERMOSTATS we give a detailed description of how room thermostats sense & respond to room temperature, and

at HEAT ANTICIPATOR ADJUSTMENT

and THERMOSTAT SWITCHES, INTERNAL we explain methods used to fine-tune thermostat operation in response to temperature swings, thus adjusting the burner on-cycle or fan operation if the heating system uses a fan.

Also see THERMOSTAT CALIBRATION where we discuss the accuracy and calibration of room thermostats.

Question: Honeywell RTH2300 thermostat not responding properly to room temperature

Office environment with a HONEYWELL RTH2300 thermostat . in Cool mode Fan On and set to 75F Hold .

cooling does not click on until 77F reached on display temp and does not click off until 73F reached on display temp

I would think cooling should click on when above 75F . . . ie at 76F . . . and click off when below 75F . . . ie at 74F

Is this operating within standard tolerance? is the thermostat defective? is there any means to rectify to hold at 75F?

Right now there is a 4 degree variance which at 77F is slightly too warm and at 73F is slightly too cool .

would be better clicking on at 76F and off at 74F.

Thought about changing the batteries but don’t think that should have any effect as cooling is clicking on and off OK and display reading OK just at higher and lower temps than the setting.
Any comments or suggestions to rectify would be greatly appreciated. 12 August 2015 Bryan

Reply: check for dirt, dust, or drafts before replacing a non-responsive thermostat

Good question, Bryan. I like the Honeywell RTH 2300 thermostat series an have installed a number of them without having the trouble you describe.

I'd expect the thermostat to respond just as you do. And I'm doubtful that batteries are the problem.

1. FIRST: inspect the thermostat closely to be sure that no clod of dust or crud is blocking the little thermistor that senses temperature.
2. SECOND: check that the thermostat is not being confused by external conditions such as location on a wall that exposes the thermostat to hotter or cooler temperatures than the actual room temp.
   
   A subtle example can be a convection current running through an uninsulated interior wall cavity that is blowing cool air into the thermostat from its back-side through the wiring opening in the wall.
   
   We discuss how to fix that problem at
   
   THERMOSTAT WIRING OPENING SEAL
   
   This is probably not your problem since if the thermostat were being thrown off by sunlight, wall mounting location, or drafts, I'd expect its room temperature to reflect that influence.
   You'd see instead a gap between the room temperature shown by the thermostat's indicator and an independent measurement of room temperature say in the middle of the room.

A programmed setting can also confuse us about how the thermostat should be responding if a thermostat is running under a program whose settings are not what we thought.

But if you've got the thermostat in HOLD mode then it ought to respond to temperature changes around the hold temperature setting. Double check that you see the word "HOLD" in the display.

This Honeywell RTH2300 thermostat has some self-diagnosing circuitry which I summarize:

• It will display low battery ("Lo Batt") for 60 days before the battery is dead.
• HI: the ambient temp is above 120F
• LO: the ambient temp is below 32F - these are the operating limits of the device
• E1 or E2 = bad sensor, replace the thermostat

I'd give the company a call to ask about the response you're experiencing:

Call Honeywell Customer Care toll-free at 1-800-468-1502 or see the company's consumer website at DIYthermostats.honeywell.com.

Also see THERMOSTAT CALIBRATION where we discuss the accuracy and calibration of room thermostats.

Steam Heat Room Thermostats, Wall-Mounted

Room thermostats used to control steam heat may vary from their cousins illustrated above, or not - depending on just what the thermostat is controlling. In a residential application a standard room thermostat works fine to turn on or off the steam boiler.

But in larger buildings you may find that the room thermostat for steam heat is controlling a valve or relay that admits steam to radiators in one room or in just one section of a building.

In our photo at left, this wall thermostat controls steam heat in a college office in Poughkeepsie, NY.

[Click to enlarge any image]

The upper scale indicates the current room temperature.

The lower dial-scale is the set-temperature adjustment on this thermostat. The thermostat controls a steam radiator valve that in turn admits or shuts off heat into the space managed by this device.

RADIATOR & BASEBOARD THERMOSTATS, Automatic - TRVs provide an alternative that can control individual hot water or steam radiators in buildings.

Thermostat Accuracy: Settings vs Room Temperature

A Guide to Using Wall-Mounted Room Thermostats - How to Set the Thermostat

This topic has been moved to its own article now found

at THERMOSTAT SET PROCEDURE

How to Set a Room Thermostat To the Desired Temperature

See THERMOSTAT SET to DESIRED TEMPERATURE

Question: Honeywell RTH 2300 thermostat in cool mode accuracy

Office environment with a HONEYWELL RTH2300 thermostat . In Cool mode Fan On and set to 75F Hold . But cooling does not click on until 77F reached on display temperature.

And cooling mode does not click off until 73F reached on the display temperature.

I would think cooling should click ON when above 75F, ie at 76F and would click OFF when below 75F, ie at 74F.

Is this operating within standard tolerance?

is the thermostat defective? Is there any means to rectify to hold at 75F?

Right now there is a 4 degree variance which at 77F is slightly too warm and at 73F is slightly too cool . Would be better clicking on at 76F and off at 74F.

Thought about changing the batteries but don’t think that should have any effect as cooling is clicking on and off OK and display reading OK just at higher and lower temps than the setting.
Any comments or suggestions to rectify would be greatly appreciated. Thanks, Bryan - 13 Aug 2015 Bryan

Moderator Reply: If the thermostat response is set to too-narrow a temperature difference there's risk of oscillation

Good question, Bryan. I like the Honeywell RTH 2300 thermostat series an have installed a number of them without having the trouble you describe.

I'd expect the thermostat to respond just as you do. And I'm doubtful that batteries are the problem.

Looking at Honeywells' FAQs for the RTH2300 the company says that the thermostat accuracy is +/- 1 degree Farenheit

Your thermostat is designed to control temperature to +/- 1 F.

How often your heat turns on and off depends on may factors including the type of heating system you have, as well as how much your system needs to run to maintain your temperature setting (in other words, how cool or cold it is outside).

A typical forced air system will cycle about five times in an hour (5CPH), this is normal.

A typical hot water system would cycle less then that.

See TEMPERATURE RESPONSE of ROOM THERMOSTATS for details.

My thermostat does not respond properly to room temperature

My capacitor, contactor and thermostat have been replaced today by me correcting the issue of the fan compressor not coming on and now my air handler fan comes on for 2-10 minutes before my fan compressor unit kicks on and then the air handler fan stays on 2-10 minutes after the fan compressor unit shuts off.

I've also noticed on the TT the unit is running to a temp lower than the temp setting by 5 degrees. 've looked everywhere on how to calibrate the setting but cant find info.

The room temp showing on TT is correct but is disagreeing with the set temp for activating unit off and on. Is it calibration of thermostat or something else? (May 27, 2014) mike

Reply:

Mike

Not all thermostats provide a heat anticipator adjustment, but older ones and many basic Honeywell and some White Rodgers thermostats do.

See these diagnostic and repair articles

• HEAT ANTICIPATOR ADJUSTMENT
• HEAT ANTICIPATOR ADJUSTMENT - T87
• HEAT ANTICIPATOR EFFECTS on ROOM TEMPERATURE
• HEAT ANTICIPATOR OPERATION
• HEAT ANTICIPATOR SET & TEST by AMMETER
• THERMOSTAT CALIBRATION

but your thermostat may be keeping things running past the set temperature for other reasons - like its location.

Check the room temperature shown on the thermostat against the set temperature on the thermostat.