Taco needs to create an animation of how the 570 series zone valve works.

@Steamhead "There was no polarity in the early days…."

Even back then, there was always a "hot" and always a "neutral", no?

And they usually fused the hot side.

Can't 100% tell, but the white neutral in the picture looks cut, maybe the receptacle to the right does not work. Maybe the wire loops under the box, it looks cut to me.

You know what is amusingly funny. The 3 wire actuator and two transformer secondaries is the same basic 120/240 circuit that powers most homes in the U.S. and Canada. It's just with the utility transformer the two secondaries contained and wired in a sealed can it is hard for others to mess it up. Each secondary has its own load and each secondary only 'Touches' the other at one point.

I'd say that's pretty damn good, Mr. Ed. I'd click the "Awesome" button, but I think it's better than that.

Nice job on this, Ed.

With a disc jockeys voice also :)

@JBarba said: it's how we can put up to three of these babies on a 40 VA transformer, even though it the valve itself has an amp draw of 0.9A, or 21,6 VA. Since that draw is not continuous, you can easily put 3 on a 40VA transformer. 

Thanks for that informatioin. I often wondered about the 0.9 Amp with 3 valves on one 40 VA tranaformer. That makes a little more sense now. I never lost sleep over it but I have wondered about it from time to time. Not like the things the really bother me like "Why is the word Abbrevation so long?" or "why we park on a driveway and drive on the Parkway. And a shipment sent by a car or truck but cargo is sent by ship?!? Those really keep me up at night.

Well I finally figured out how to actually render the video directly from the OpenToonz software app. This is a much better quality video

That would still blow the transformers if you got the wires crossed at the boiler. Isolation relays are not that expensive.

@Steamhead said: That would still blow the transformers if you got the wires crossed at the boiler. Isolation relays are not that expensive.

And all I have to say about that is: the relay is unnecessary.

You can still cross the wires between zone valve terminals #2 and #3 that go to the relay and blow transformers.

You also add load to the transformer, so now you can no longer have three valves per 40 VA transformer. Adding the load of that relay to the zone valve transformer uses up more current and can end up overloading the transformers.  Here is an example of how it works without isolation relays:

This is how I might see your Isolation relay design:

This works just as well with the additional relays. However in the next diagram you will see the common mistake where the zones are connected identically and wvwn with the isolation relays there is still a short circuit when zone thermostat all the way to the left is calling for heat.

This is how @Steamhead might reconnect a thermostat on a repair to a system I installed . That is because Steamhead is correct in his diagram, where R on the transformer is connected directly to #1 on the zone valve the way he was taught many, many …many years ago.

If all the other valves were connected the same way, with R connected directly to #1 on each zone valve, then there would be no problem.

The problem arises when @Steamhead comes across a system wired the way I teach it, where R on the transformer is connected to R on the thermostat, and he does not double-check to see how all the other valves and thermostats are wired.

Then @Steamhead ’s correct way of doing this somehow causes the transformer to fail, even with isolation relays in place, as shown below.

I’m not saying that @Steamhead is wrong . I’m saying that when troubleshooting three-wire zone valves, the way you were taught is not necessarily the same way everyone else was taught.

There is more than one correct way to wire zone valves. You just need consistency across the entire system that you are working on.

Same difference, @Steamhead , whether you have one relay for each valve or one relay for all of the valves. The wires must be consistent across the system.

I like to use R on the transformer to R on the thermostat. You like R on the transformer to #1 on the zone valve. Both work fine when they are consistant

If you mix both of our methods on the same system, you will have smoked transformers, regardless of the relay.

All the relay does is move the problem. It makes sure the inconsistency does not damage the control’s transformer, but the wiring inconsistency is still there.

The best way to solve this problem would have been for Taco to determine, 50+ years ago, that the transformer R, or non-grounded source, gets connected to R on the thermostat in their diagram.

But that will never happen, because it would make too many existing systems obsolete. It would, however, make adding smart thermostats that need a common, or C wire, much easier to retrofit.

Anyone who comes across a system wired where R from the transformer is connected directly to the zone valve needs to have the system completely rewired so every zone valve is connected the same way: R on the transformer to R on the thermostat, W on the thermostat to #1 on the zone valve, and the #2 terminal, common both circuits in the valve head, on the zone valve connected to C on the transformer.

It all fits together perfectly when it is done that way.

But if you have a six-zone-valve system, that is an expensive rewire just to add one Nest or ecobee thermostat to your home.

I like the relays for a couple of reasons.

If you go on a no heat call and walk up the boiler and the idiot light on the relay(s) is lit and the boiler is cold or not running, you have a boiler problem.

If the relay is not lit you have a zone valve thermostat or transformer issue or wiring issue.

It also eliminates an issue with two transformers tied to the same circuit (even though there is no issue it is less complicated)

I like those zone valves because the actuators are easy to change and that series of valves usually has a higher Cv rating than other valves of the same pipe size.

I do prefer an isolated end switch, however.

So IMHO easier to troubleshoot with relays.

Well the way I see it, all @EdTheHeaterMan, @Steamhead, @EBEBRATT-Ed, @hot_rod all have valid points.

IMO you don't need a relay to make the circuit work properly. Any more than you need a relay to add a new TV to your home. The circuit comparison is more similar than you may think.

What I don't like about adding things that are not actually needed for proper operation is it complicates the wiring and increases the cost, initially and to run, and more stuff to fail. Making it more complicated is just making it more complicated for the next guy. If you left a perfectly good working (neatly wired) circuit and the next guy screws it up, well that is on them, not you. Also LED indicators like the RIB has can and do fail, trust your meter that you verified before each use and not the indicators.

To me if you are going to go with the added relay circuit topology, use a zone valve controller, since it simplifies the wiring, provides isolation and activity indication, but it has a cost.

The one thing I find sad about the original @JohnNY post is this circuit is not that complicated. I hope that electrician never has to troubleshoot Polyphase equipment issues.

Was this inoperative zone valve issue ever resolved ??? If so, what was found ?

You can wire anyway you want that works. I have wired them with relays and without.

What I am saying is that by using relays it more closely follows the wiring of a 4 wire valve where the valve power and its opening and closing is controlled by 1 circuit and the burner control is isolated by an end switch or in the case of these Taco valves by a relay.

I am simply trying to "dumb it down" as the average "technician" on the street is not going to have a clue what to do with these valves especially with multiple valves on one boiler.

Strangely if I remember right Taco does not describe the operation of the valve or its (two transformer) integration in the install instructions.

It is in the sales brochure which most technicians are not going to know to access that while on a service call.

Not a big fan of ;

The average technician should learn their trade, the information is not hard to find if you look.

Be above average.

This install instruction shows this wiring diagram only. As previously stated the theory of operation is not in this document. But it is out there and most any technician has a phone that it could be found with. Technicians should be able to do research as needed.

I don’t know of many, any, hydronic components that don’t come with installation manuals. Especially controls.

Or many techs that don’t have phones or tablets with them?

Many manufacturers gave short online videos for non readers

Shop have internal training sessions presented by reps and manufacturers.

If the technician goes into the field without training or access to a senior at the company, a txt of phone call away… whos fault is that?
Especially in the case if a 570 valve, been around what 50 years!

@EBEBRATT-Ed, maybe the average Tech should wire it exactly as shown in the installation manual, no need to read the theory of operation. Then they can be amazed it works. Then in their amazement maybe they will do the research as to understand why it actually works. Or they can just not care and move on to the next task.

And if the average Tech is that inept why would they think of adding a relay in the first place ?

Oh my the windings are connected together. It can't work, but it does. How does it work ?

I realize a 3 phase example is a bit beyond the scope of wiring zone valves and thermostats. It is an easy example of secondaries connected together.

Another common example is the center tapped secondary or actually the two secondary windings of the common 120/240 electric utility transformer that powers most homes in North America. Homes are not littered with relays for every device plugged into a receptacle. There is more mechanical structure to wiring a house, but the electrical part is basically the same.

Besides even with adding relays you still can get smoke.