Honeywell T87F Thermostat wiring diagram for 2-wire, spst control of heating only in a typical gas fired heating system - details from Honeywell Controls Room thermostat wiring diagrams for HVAC systems
     


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Thermostat wiring schematics: this article provides room thermostat wiring diagrams for Flair, Honeywell, White Rodgers and other thermostat brands.

For people who prefer to see an actual wiring schematic or diagram when wiring up a room thermostat, those illustrations are provided here to help understand what wires are being connected and what each wire is doing.

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Room or Wall HVAC Thermostat Wiring Diagrams

Honeywell T87F Thermostat wiring diagram for 2-wire, spst control of heating only in a typical gas fired heating system - details from Honeywell ControlsArticle Contents

We recommend following the instructions provided by the manufacturer for your specific thermostat, as wiring details may vary. Also at least some manufacturers' instructions call for installation of the thermostat by a qualified technician. And in the tables given in the article above you will find explicit wiring instructions for most common room thermostats.

Nevertheless, in response to reader interest we include here examples of actual wiring diagrams or wiring schematics for common wiring diagrams for heating and cooling thermostats including Honeywell diagrams for heating & cooling thermostats and the thermostat connections for White Rodgers & other brands of thermostats.

Argo AR61 Triple Aquastat Switching Relay Thermostat Connections & Wiring Diagrams

At left the wiring diagram illustrates the Argo AR61 triple switching aquastat equipped to connect with three thermostats. Unlike the remaining wiring diagrams in this article, the AR61 is a controller, not a thermostat. In our photo at right you can see the three thermostat terminal connection pairs.

This controller can control multiple circulator relays and is also used with tankless coil boilers and cold-start boilers - options reflected in the wiring diagrams, below left.
[Click any image or thermostat wiring schematic to see an enlarged, detailed version]

Flair 2-wire thermosat wiring diagram Flair 2-wire thermosat wiring diagram

Honeywell's L8124A,C and 8151A are triple aquastats similar in function, often used to control zone valves.

Flair Thermostat Wiring Diagrams

2-Wire Flair APOV2 Thermostat wiring diagram

Flair 2-wire thermosat wiring diagram At left the thermostat wiring diagram illustrates use of a Flair APOV2 wall thermostat in a typical 2-wire application controlling a heating appliance.

In this application the thermostat is acting as an spst (single pole single throw) switch to turn heat on or off, often by operating a zone valve.

When used to operate a zone valve the thermostat wires are connected to the zone valve terminals, not to a primary control on the heating boiler.

[Click any image or thermostat wiring schematic to see an enlarged, detailed version]


Flair 3-wire thermostat wiring controlling a zone valve

3-Wire Flair APOV2 Thermostat wiring diagram

At left the thermostat wiring diagram illustrates typical use of a Flair APOV2 wall thermostat in a 3-wire application controlling a heating appliance.

In this application the thermostat is acting as a single pole double throw (spdt) switch to control heating & cooling or in some zone valve applications.

Also see our table of Flair thermostat wiring connections found above at

Honeywell Thermostat Wiring Diagrams

2-Wire Gas Heat Honeywell T87F Thermostat wiring diagram

Honeywell T87F Thermostat wiring diagram for 2-wire, spst control of heating only in a typical gas fired heating system - details from Honeywell Controls

At left the thermostat wiring diagram illustrates use of a Honeywell T87F thermostat in a 2-wire application controlling a gas fired heating appliance.

In the Honeywell T87F thermostat series the single pole double throw switch makes (closes) one set of contacts when the temperature falls - to turn on the heating appliance.

A second set of contacts will make or close on temperature rise. This second set of contacts is typically used to operate a cooling or air conditioning system but may also be used to operate other controls or valves in some heating systems.

[Click any image or thermostat wiring schematic to see an enlarged, detailed version]


Honeywell T87F Thermostat wiring diagram for 2-wire, spst control of heating only in a typical gas fired heating system - details from Honeywell Controls

2-Wire Oil Heat Honeywell T87F Thermostat wiring diagram

Above the thermostat wiring diagram illustrates use of a Honeywell T87F thermostat in a 2-wire application controlling an oil fired heating appliance.

For a table of wiring connections for this thermostat also see Two-Wire Honeywell T87-F type Wall Thermostat wiring

3-Wire High Limit Honeywell T87F Thermostat wiring diagram

Honeywell T87F Thermostat wiring diagram for 2-wire, spst control of heating only in a typical gas fired heating system - details from Honeywell Controls

At left the thermostat wiring diagram illustrates use of a Honeywell T87F thermostat in a typical 3-wire, open contact, high limit control such as on an oil fired heating boiler.

 

 


3-Wire SPDT Honeywell T87F Thermostat wiring diagram

Honeywell T87F Thermostat wiring diagram for 2-wire, spst control of heating only in a typical gas fired heating system - details from Honeywell Controls

At left the thermostat wiring diagram illustrates use of a Honeywell T87F thermostat in a 3-wire application as a spdt (single pole double throw) switch such as used to control low voltage motors, electric radiator valves, zone valves.

The thermostat makes a contact on both a rise and on a fall of room temperature.


4-Wire Honeywell RTH2300 5+2 Programmable Thermostat wiring

Honeywell RTH2300 Thermostat wiring diagram for 2-wire, spst control of heating only in a typical gas fired heating system - details from Honeywell Controls

At left the thermostat wiring diagram illustrates the typical wiring connections when installing a Honeywell RTH2300 (or similar) programmable room thermostat. Be sure to identify and label the existing thermostat wires before disconnecting them from the terminals on the old thermostat you are replacing.

Watch out: existing thermostat wires that will not be used in the new thermostat installation, such as wires attached to C or C1 terminals on the old thermostat should have their ends taped so as not to accidentally touch and short other thermostat wires or connectors.

Need More help? Call Honeywell at 1-800-468-1502 for assistance with your Honeywell thermostat.


Honeywell Series 10 Thermostats & Controls

Honeywell Series 10 control schematicHoneywell Series 10 controllers such as the Honeywell R19A use a simple relay and built-in transformer and one or more line voltage contactors.

These are spst switch type controls (such as heat-only).

The No. 1 is a low voltage holding contact while the No. 2 is a line voltage contactor. The "coil" shown may be a magnetic coil that pulls in the armature of the No. 1 relay or it may be a relay type coil used in a gas control valve. The holding contact closes when the coil is energized.

In this sketch from a 1949 Honey Heating Control Handbook the thermostat has been satisfied (both contacts are open) and the system is not calling for heat. On a drop in temperature the flexible blade makes the white contact, and subsequently connects the stiff blade. On a rise in temperature the contacts break (or open) in the opposite order. [Line voltage circuits are not shown].

Symptoms of Broken or Shorted Thermostat Wires in a Series 10 SPST type circuit

Understanding the wiring details of series 10 controls and circuits can help us diagnose heating and cooling system operating snafus. Here are more examples from the Handbook.[12]

Symptoms of an open thermostat wiring circuit (broken wire, bad splice, loose screws)

  1. White wire broken: thermostat cannot pull in the relay and cannot hold it open - after a momentary shorting of the W-B terminals at the relay or valve
  2. Blue wire broken: thermostat cannot pull in the relay or valve, but once the relay is forced in (closed) the circuit can hold
  3. Red wire broken (or a loose heater plug screw) causes short cycling on the blue contact - single point operation

Symptoms of a short circuit in the thermostat wiring

  1. White wire shorted to the blue wire: relay or valve stays "on" unless all electrical power is shut off by the limit control switch, by disconnecting a wire at the low voltage transformer, or by turning off power to the system
  2. White wire shorted to the red wire: thermostat can start the heater's burner but can't stop it
  3. Red wire shorted to blue wire: short cycling (single pointing) on the white contacts alone

Mis-wiring of thermostat wires: wires connected to the wrong terminals

  1. White & blue wires swapped incorrectly: causes short cycling on the blue contact
  2. Blue and red wires swapped: short cycling on the white contact
  3. Red and white wires swapped: normal operation except that the heater is effective too quickly - resulting in short on-cycles and inefficient operation

White Rodgers Thermostat Wiring Diagrams for 2, 3, 4, and 5-Wire Hookups for Heating & Cooling Applications

The White Rodgers 1F90 and similar models will replace most 2-wire heating thermostats and many 3-wire & 4-wire thermostats used for both heating and cooling. It is not used on systems without a transformer or relay, hot water heat systems that use 3-wire zone valves, two-stage heating or cooling systems, and certain other applications. [See the installation instructions for other examples.] A nice feature of this system is that the user can adjust the heating or cooling cycle-on time, and provides features similar to adjusting the heat anticipator in older Honeywell thermostats.

White Rodgers 2-Wire Heat Only Thermostat wiring diagram

White Rodgers 4-wire 1F90 thermostat wiring diagram2-Wire Heat-Only White Rodgers thermostat wiring detail for a White Rodgers 1F90 Low Voltage Digital Comfort-Set thermostat

Also see our tables of White Rodgers thermostat connections above at

 

 

 

 


White Rodgers 3-Wire 1F90 Heating Thermostat wiring diagram

White Rodgers 4-wire 1F90 thermostat wiring diagram3-wire heating-only wiring details for a White Rodgers 1F90 Low Voltage Digital Comfort-Set thermostat

 

 

 

 

 

 

 


White Rodgers 4-Wire 1F90 Thermostat wiring diagram

White Rodgers 4-wire 1F90 thermostat wiring diagram4-wire heating & cooling applications using a White Rodgers 1F90 thermostat

 

 

 

 

 

 

White Rodgers 5-Wire 1F90 Thermostat wiring diagrams

5-Wire heating & cooling control wiring using a White Rodgers 1F90 thermostat

White Rodgers 4-wire 1F90 thermostat wiring diagram White Rodgers 4-wire 1F90 thermostat wiring diagram

Want Help with Thermostat Wiring or Installation?

  • Thermostat Wiring help: If you need help figuring out the wiring for your thermostat see the instructions that came with your unit, or if you can't find the instructions (the dog ate the thermostat installation guide), see our detailed thermostat wiring guides at
  • Thermostat Switch Setting Help:
  • Help from the Thermostat Manufacturer
    • 3M customer help line: 1-888-607-5824 for the Filtrete thermostat . Watch out: the Filtrete™ 3M-22 is a battery-operated thermostat. If the batteries fail the thermostat may fail to provide heating or cooling and the building may suffer accordingly.
    • Emerson Technologies (White-Rodgers products): http://www.emersonclimate.com (they don't seem to want you to call)
    • Honeywell customer help line: 1-800-468-1502
    • Robertshaw customer help line: 1-800-304-656

 

 

Continue reading at THERMOSTAT INSTALLATION STEPS or select a topic from the More Reading links shown below.

Or see At THERMOSTAT WIRE CONNECTIONS - tables matching thermostat wires by color or label to their thermostat connections.

Or see THERMOSTAT WIRE FUNCTIONS

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THERMOSTATS, HEATING / COOLING at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

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