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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.
At THERMOSTAT WIRE CONNECTIONS we provide tables matching thermostat wires by color or label to their thermostat connections. We also provide a separate explanation of THERMOSTAT WIRE FUNCTIONS. Separately at THERMOSTAT INSTALLATION STEPS we provide a step by step photo guide to installing a room thermostat.
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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.
Honeywell's L8124A,C and 8151A are triple aquastats similar in function, often used to control zone valves.
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]
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
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]
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
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.
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.
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.
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.
Symptoms of an open thermostat wiring circuit (broken wire, bad splice, loose screws)
Symptoms of a short circuit in the thermostat wiring
Mis-wiring of thermostat wires: wires connected to the wrong terminals
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.
Also see our tables of White Rodgers thermostat connections above at
5-Wire heating & cooling control wiring using a White Rodgers 1F90 thermostat
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