HVAC systems with more functions need more wires to communicate to and from the thermostat. Over a long distance, the signals can become to weak to get a reading. Note 1. 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. If you decide to get rid of your outdated thermostat for a smart or wifi thermostat, be sure to mark the wires to indicate which color letter on the board they are connected to. In addition to providing concise details of nearly different boilers fuelled by electric, gas, oil and solid fuel, and over programmers and time switches, this invaluable resource also features numerous easy-to-understand wiring diagrams with notes on all definitive systems. Our page top sketch, courtesy of Honeywell Controls, illustrates the wiring diagram for a traditional Honeywell T87F thermostat used for 2-wire single pole single throw control of heating only in a typical gas-fired heating system.
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The Thermostat Wiring Color Code Guide
Try the search box just below, or if you prefer, post a question or comment in the Comments box below and we will respond promptly. 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. Red wire coming to the thermostat from transformer secondary R terminal. Illustrated here: There are a variety of thermostat wire types.
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