Honeywell heating zone valve Heating Zone Valve Wiring
How to wire up a heating zone valve

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Hot water heating system zone valve installation:

This article describes how to wire up heating zone valves. 

We include wiring diagrams and installation instructions for most zone valve model and multi-zone controllers, and we describe special wiring problems that can occur if you mix different types, brands, or models of heating zone valves on the same hydronic heating (hot water heating) system.

We also provide a MASTER INDEX to this topic, or you can try the page top or bottom SEARCH BOX as a quick way to find information you need.

Zone Valve Wiring Hookups for Hydronic (Hot Water) Heating Systems

Taci ZVC493 wiring diagram - click to enlarge - at InspectApedia.comIndividual Hydronic Heating Zone Valve & Control Wiring Notes by Brand

Illustration: the wiring diagram for the Taco ZVC 403 Multiple-Zone-Valve Controller. [Click to enlarge any image] - be sure to check the exact wiring diagram for your particular control and application.

Taco SR502 Two Zone Switching Relay Wiring Chart at

Above: wiring example for the Taco SR502 two-zone switching relay. See the SR502 instructions for important details and safety warnings. [Click to enlarge any image]

Taco SR503 Three Zone Switching Relay Wiring Chart at

Above: wiring example for the Taco SR503 three-zone switching relay. See the SR503 instructions for important details and safety warnings. [Click to enlarge any illustration]

Taco SR503-4 Zone Switching Relay Control - wiring diagrams and installation instructions given here at InspectApedia along with contact information for Taco

Also see

How to Wire Multiple Taco SR502-SR506 Switching Relays

How to wire two Taco switching relays in series to control up to 8 heating zones - at

To control up to eight heating zones you might wire multiple standard switching relays together as shown in this TACO wiring diagram. This illustration is from the TACO SR503-4 Switching Relay Instruction Sheet whose link is given above. [Click to enlarge any image]

Watch out: Be sure to see important instructions and safety notes in that document.

Question: Having trouble wiring up different zone valve controller brands together

Mixed brand zone valve wiring schematic (C) Daniel FriedmanHi, I have a HE II Weill McClain natural gas boiler.

A few years back I converted about 1/4-1/3 or my house into hydronic radiant floor heat running off same zone as the baseboard. The guy who sweated the tubes and zoned it out has never come back to hook up the zone controller.

Schematic at above-left: wiring hookups for a mixed-brand zone valve installation: Honeywell & White Rogers. Click to enlarge any image or schematic.

Someone else came out the other day to hook it up. I have a TACO SR502 2-zone controller and this person purchased a Honeywell L6006C 1018 aquastat controller.

I am thinking he purchased the wrong aqua stat.

He said the whole system will never allow for 2 zones. [Click to enlarge any image]

I spoke w/techs @both TACO and WeilMcClain who, both said, I can have my floor heat operate separately from the BB units.

(I do have 2 thermostats).

Can you shed a little light on this, please? Thanks, - T.B. 10/27/2013

Reply: known problem; Example of Wiring Different Brands of Zone Control in Same System

Absolutely, if properly wired, you can take a single loop of hot water baseboard heat and subdivide it, giving each sub-loop its own thermostat and zone control valve.

Properly wired, the individual thermostat calls for heat, the zone valve opens, when the valve is fully open an end switch in the valve connects a second pair of wires that turn on the circulator pump back at the boiler.

Photo below, (reader contributed) illustrates typical wiring connection at two zone valves.

Zone valve wiring, multiple zones (C) InspectApedia On most U.S. systems the circulator runs sending water through the open zone loops and a primary control at the boiler, monitoring water temperature, actually turns the boiler on or off as needed to re-heat the water.

In addition to your control, the Honeywell L6006C 1010, Honeywell's L8124A,C and 8151A are triple aquastats similar in function, often used to control zone valves. Where you can run into trouble is with an installation that has a mix of different brands of zone valves. In that case, the wiring instructions for one company may be different from the other.

When I got into that trouble years ago I was wiring up a Honeywell zone valve to a system already using Flair zone valves. I called my heating supplier who had Dave Ferris (now retired) on deck to answer wiring questions.

The solution was trivial once Dave said - Just hook the red wire to terminal "x" and the yellow to "y" and so on.

My ugly rough sketch above on thi spage needs to be re-drawn neatly, but there I show how we successfully wired-up a mixed brand zone valve installation. I had two Honeywell zone valves and one White Rogers zone valve. [Click to enlarge any image].

Watch out: in wiring the mixed-brand zone valves shown in my sketch above, it is important that

The correct wiring depends on the zone valve models.

Without Dave the next-best is to look  with care at the instructions that came with the zone valves, and at the wiring diagrams for hook-up instructions; if you are left still confused, the manufacturer will know how to hook-up.

More about wiring Taco zone valves - see TACO ZONE SENTRY VALVES[PDF] installation instructions

Zone Valve Compatibility Notes

Typical zone valve installation at a heating baseboard - Flair Corporation adapted by InspectApedia The Flair and White Rogers are compatible with one another with no special tricks

Watch out: The Honeywell zone valves are NOT compatible with Flair and White Rogers unless you follow careful wiring details.

I give an example above, but you may need to review wiring with the manufacturers of your zone valves.

In fact Zone-A-Trol zone valve installation instructions carried this warning:

Zone-A-Trol Valves should not be wired in the same circuit with zone valves of a different make or manufacturer without first consulting your local Zone-A-Trol representative or our factory engineering department for special wiring information. [2]

Master Control & Zone Valve & Thermostat Wiring Connection Tips

The thermostat wires on the master (primary) control will show about 20-volts from the on-board thermostat relay transformer inside the primary control.

No voltage should be presented by the zone valves, thermostat, or transformer circuit TO the primary Controller.

We see 24-volts through the zone controllers and transformer but Zero voltage on the zone valve end switch wires that go to the thermostat TT terminals on the master or primary control.

Reader Question: how many zone valves can be connected to a single thermostat?

3/5/2014 tej said: how many zonal valves for floor heating can be connected to one room thermostat

This question originally was posted at ZONE VALVES, HEATING

Reply: use of a switching relay to control multiple devices from a single thermostat

Normally one thermostat controls one heating zone and is connected to one zone valve. But as the thermostat is basically an on-off switch, indeed we've discussed with readers the successful combining of more than one zone valve switched by the same thermostat.

Watch out: to avoid overloading the tt or its power or circuit, check the zone valve wiring instructions. For switching multiple zone valves with one thermostat you may need to have the thermostat control a switching relay that in turn switches the gang of multiple zones. A typical switching relay such as the Taco SR502 - 506 can swit3ch 4 zone valves or more.

To find out more about the Taco switching relays I cited contact

Taco Inc., 1160 Cranston Street, Cranston, RI 02920 Telephone: (401) 942-8000 FAX: (401) 942-2360 - USA

or if you are in Canada contact
TACO (Canada), Ltd., 8450 Lawson Road, Unit #3, Milton, Ontario L9T 0J8. Telephone: 905/564-9422. FAX: 905/564-9436.

The company's website is at and their wiring guide is at

Honeywell Zone Valve Wiring Wire Colors

General Honeywell Zone Valve Wiring instructions (just below) are followed by links to Honeywell Zone Valve Instruction Sheets

Typical zone valve yellow & red wire connections:

Honeywell zone valve wire sketch (C) Daniel Friedman

[Click to enlarge any image]

Honeywell zone valve wire sketch (C) Daniel Friedman





Above Honeywell zone valve wiring diagrams are from Honeywell's motorized [zone] valve installation instructions [3]

Watch out: when installing zone valves not to overheat the valve or its parts. We were taught to completely remove the zone valve motor and electrical parts while sweating the zone valve to the heating system piping, but even so, overheating can damage the zone valve moving parts or o-ring seals. Honeywell warns not to use silver solder when sweating zone valves because of the higher temperatures required with silver solder.

Honeywell Zone Valve Instructions

Flair Zone Valve Wiring Connections at the Thermostat & at the Zone Valve

From Flair Manufacturing's original installation instructions for the Flair Zone-A-Trol we include these wiring details. The Flair Zone-A-Trol valves in the company's wiring diagrams are typically shown wired in parallel.

How Are Multiple Zone Valves Wired?

On installations where it is not convenient to wire from valve to valve as in the diagram, a separate 3-color wire conductor can be run from terminals 1, 2, 3 of each zone valve to a convenient junction point.

By observing and respecting the color codes, conductors from corresponding-numberd terminals of each zone valve may be joined or spliced together and a single conductor may be conducted from that splice to the appropriate power and control terminals shown in the wiring diagram.

Wiring the Zone Valve:

Wiring the Thermostat with this zone valve

Watch out: when connecting wires to terminals at the zone valve and at the thermostat or any other control, do not let the stripped end of the wire touch or short out against any other wire or terminal.

Flair zone valve hookup schematic (C) Daniel Friedman

Multiple zone valve wiring

Below we illustrate how a "gang" of Flair zone control valves would be wired-up.

Flair zone valve hookup schematic (C) Daniel Friedman

Flair zone valve hookup schematic (C) Daniel Friedman

See this image for Complete and detailed wiring diagrams for FLAIR 2-WIRE ZONE-A-TROL VALVES. [image] An example from that page is shown just below.

See this image for Complete and detailed wiring diagrams for FLAIR 3-WIRE ZONE-A-TROL VALVES [image]

Flair zone valve wiring for 2-wire thermostats

Flair Zone Valve with 2-Wire Thermostat: wiring diagram

The Flair control wiring diagrams below are excerpted from THERMOSTAT WIRING DIAGRAMS

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 to see an enlarged, detailed version]

Flair 3-wire thermostat wiring controlling a zone valve

Flair Zone Valve with 3-wire 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

The table below is an excerpt from THERMOSTAT WIRE CONNECTIONS

How to Wire a typical Flair 3-wire type Wall Thermostat

(3 wires found in use at the wall thermostat)

Flair model ANOVO Thermostat fed from a Flair zone valve

As wire colors may vary, note the wire colors Wire coming from Flair zone valve terminal (4) "Open" . Note 1.
At the Flair zone valve and Wire coming from Flair zone valve terminal (5) "Common"
Match those colors to terminals at the thermostat as shown here Wire coming from Flair zone valve terminal (6) "Closed"


1. The [Honeywell 5-2 Day Programmable Thermostat - RTH2300B1012] thermostat cannot be used if your old thermostat had and used any two of the following wires: R, RC, RH, 4 and V.[5]

More Flair Zone Valve Wiring Instructions Diagrams

Reader Question: Adding a third heating zone with its own zone valve

I am adding a third zone (basement) to my oil fired hot water baseboard heating and have it all planned as far as the plumbing is concerned.

The add-on heating zone will have it's own 24V zone valve so will require a wall mounted thermostat. I'm only looking for heat so I believe a 2 wire thermostat is sufficient. My other two zones have their own valves and thermostats and the wiring at the valves is all connected with wire nuts and doesn't make any sense to me.

I guess my question is, can I just connect my new valve and thermostat directly to the aquastat terminals that "appear" to power the other valves and thermostats ?

If so, is there anything I need to be aware of, like possibly wiring it backwards and frying something ?
If I can just add the new "loop" directly to the aquastat, in what order are the connections made ? Example, aquastat to one connection at valve, 2nd connection at valve to one connection at thermostat, other connection at thermostat back to aquastat ?

If you need me to provide more detail on the types of thermostat, aquastat and zone valve I am using I can. My zone valve has two red wires and two yellow wires. The instructions seem to indicate that I only use the yellow wires and the red wires were for auxiliary, whatever that is. Would much appreciate your input. Thanks. - Will 11/10/11


Will I think this will help clear things up a little for wiring a 3rd heating zone using a zone valve approach:

When the TT calls for heat (yes 2 wire is fine) it tells the zone valve for its zone to OPEN. When the zone valve is fully open it in turn tells the circulator pump to start pumping. (There is an "end switch" in the zone valve that performs this second function).

So you'll find a pair of wires from TT to the zone valve and a pair of wires from the zone valve to the circulator relay.

Watch out though: the wiring connections can vary a bit among zone valve brands - if all of yours are the same brand you can look at the existing valve, follow the wires, and you'll see how the zone valve is hooked up. If there are different brands you'll need to ask for a clue from your HVAC supplier or the manufacturer.

Reader follow-up:

Dan, thanks for the information. So I effectively have two circuits to connect. One 24v circuit runs in series as follows - transformer, zone valve, thermostat, transformer. Please can you confirm this.

The other circuit is simply connecting the other two wires on the zone valve to the connections on the circulator relay.

For the first circuit, do you know where my transformer is likely to be located ? I have the box on the front of my furnace which contains controls for how hot the water gets and when it needs to be heated. Would it be in there ?

For the second circuit to the relay, I'm assuming the relay is attached to the circulator pump itself.


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