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THERMOSTATS, HEATING / COOLING
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ZONE VALVES, HEATING
Thermostat wiring details & connections for nearly all types of Honeywell room thermostats used to control residential heating or air conditioning systems. This article gives a table showing the proper wire connections for Honeywell brand wall or room thermostats used to control heating or air conditioning equipment. Other thermostat wiring schematics are provided by this article series and are listed at THERMOSTAT WIRING CONNECTION TABLES.
Room thermostat installation & wiring guide: this article series explains the basics of wiring connections at the thermostat for heating, heat pump, or air conditioning 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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Remember that ultimately a thermostat is simply an on-off switch, or provides several on-off functions. But with multiple zone heat, you should expect to provide a thermostat for each individual zone - else they're not heating zones at all.
In a traditional hot water heating system that does not use the Azel i-Link controller, the first thermostat is wired directly to an aquastat that controls the first zone; the second two thermostats are wired to individual circulator relays (if individual circulator pumps are used) or to individual zone valves (if a single circulator runs the whole system).
Where zone valves are used, an end switch closes to turn on the circulator (a logical inclusive OR function with the other zone valves) when the zone valve opens to allow hot water to flow. That same principle is used when wiring the Azel i-Link Zone Switching Relay. And the company makes clear that their controller is compatible with standard thermostats:
First let's make sure you've identified your Honeywell thermostat model correctly.
Honeywell RHT2300B - the number you gave, doesn't look right, but you probably meant RTH-2300-B. Calling Honeywell with the right product number (Tel: 800-468-1502) might produce better results. Honeywell has done a great job making installation and operations manuals available for their equipment, but you've got to search with the right product number.
Searching the Honeywell site for the corrected thermostat number delivers a single product that's probably yours, the 5-2 Day Programmable Thermostat - RTH2300B1012. In fact this thermostat is widely sold including at Home Depot stores, and I've installed and used this very model myself to control an add-on hot water heating zone and Taco circulator in an older home. According to Honeywell, this thermostat is compatible with:
For your model you want Honeywell document 69-2326ES - found at http://customer.honeywell.com/Honeywell/getliterature.axd?LiteratureID=69-2326ES.pdf - owners operation manual or
document 69-2327ES - for installation materials - found at
Here are details from that manual's instructions for wiring the Honeywell RTH-2300-B 5-2 Day Programmable Thermostat beginning with the inspection of the existing wires:
How to Correctly Identify the existing thermostat wires
3. Identify and label each of the existing thermostat wires by using not the wire colors (someone could have made a wire color error and violated convention) but rather, identify each existing thermostat wire by noting the letter next to the old thermostat wiring block terminals where each wire was connected to a screw. Identify and label the wires that are connected as
If any wires are not attached to your old thermostat or are attached to a terminal marked C or C1, they will not be connected to your new thermostat. Wrap the bare metal end of each of these wires with electrical tape, so it cannot touch and short other wires.
Watch out: since here we are focusing on connections, I am leaving out some important procedure and safety details like removing and taping each wire end to avoid shorting, etc. so be sure to consult the installation manual in detail.
On your new thermostat, the Honeywell the 5-2 Day Programmable Thermostat - RTH2300B1012, connect the wires you labeled as follows:
Honeywell 5-2 Day Thermostat Wiring Table: If the wire labels from your old thermostat hookup don't match the above, Honeywell offers additional advice that we adapt in table form provided in detail at Honeywell 5-2 Day Programmable Thermostat - RTH2300B1012 wiring.
If the wire labels from your old thermostat hookup don't match the above, Honeywell offers additional advice that we adapt in table form:
We provide thermostat wiring connections for just about every type of residential heating or cooling room thermostat as well as a description of thermostat wiring color codes & conventions. At THERMOSTAT INSTALLATION STEPS we provide a step by step photo guide to installing a room thermostat. We also provide THERMOSTAT WIRING DIAGRAMS and a separate explanation of THERMOSTAT WIRE FUNCTIONS or select a topic from the More Reading links shown below.
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Frequently Asked Questions (FAQs)
Question: Replacing a round Honeywell T87 with a Digital Honeywell Thermostat
Hello - I am replacing a round Honeywell thermostat with a non-programmable digital Honeywell unit. I have a hot water system with multiple zones and with no air conditioning. There are three wires at the thermostat. On the old round unit the red wire went to the R terminal, the white wire went to the w terminal and a green wire went to B terminal. I hooked up the new stat the same way but it would not work. If I selected "fan on" instead of "fan auto" the zone would heat up but would not shut off (hot water kept flowing even if I selected a temp below room temp). Appreciate your help. - Patrick - 1/20/12
Patrick, typically the three wire thermostat hookups would be exactly the same for the old and new thermostats.
For details of wiring a typical and simple digital Honeywell thermostat, see Honeywell 5-2 Day Programmable Thermostat - RTH2300B1012.
For help in understanding the wiring of your old thermostat, see Three-Wire Honeywell Wall T87-F type Thermostat wiring and also see Generic HVAC Thermostat Control Wiring Points
Question: Replacing a mercury thermostat with a digital unit
I am replacing an old mercury thermostat with a digital. my system is a heat pump. my neighbor gave me the digital, no instructions, no box. i'm trying to decide if this is even a heat pump compatible thermostat. on the therm it has c, g, rc, rh (which are linked by a black wire.) w, y, b, and o. coming out of my wall is, white connected on old therm w2, yellow connected to y, green conn g, black conn e, red to r, blue to b and bro to x. any help would be great. - Kurt 6/4/12
Kurt, as you see in the examples at For help in understanding the wiring of your old thermostat, see Three-Wire Honeywell Wall T87-F type Thermostat wiring and also see Generic HVAC Thermostat Control Wiring Points. Many thermostat wiring setups are straightforward or "cookbook" but why not find the brand name on your thermostat and then you can obtain the installation instructions right from the manufacturer?
Also, Honeywell's thermostat replacement advice (and most likely that of all thermostat manufacturers) warns:
Watch out: MERCURY NOTICE: Do not put your old thermostat in the trash if it contains mercury in a sealed tube. Contact your local waste management authority for instructions regarding recycling and proper disposal.
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