Why is thermostat/zone valve wiring not done neater?

The Taco 571 would have 4 terminals Two for the motor and a dry contact end switch. In your diagram your showing a three terminal . Which is a power on and power off zone valve . You need a analog double contact thermostat . In the diagram you are trying to phase three transformers , the relay is the third .

@Big Ed_4 , you're thinking of the Taco Zone Sentry which uses a ball valve. The 571 has the 3-terminal heat motor.

Qne would be the hot for the motor , two would be a joint common and two and three would be the end switch to the relay ?

I just checked out a wiring diagram ..

To answer your question, everyone wires their zones differently and since most hydronic installers don’t have the rigorous training that electricians have, it’s often messy and counterintuitive. 
Yes, the SR501 is only a pump control and you have to freehand the zone valve wiring while the ZVC's combine zone valve wiring AND pump wiring all in one unit.

Normally, 3 is just a dry contact that joins 2 for end switch closure, no?

1 is hot
2 is common 
2 and 3 are end switch 
no??? 

No one knows for sure why it was done the way it was except the guy who did it.

On another note: the Nest is not a good choice for a hydronic system.

If you want to save some money and do a little more work you could get some terminal strips and a piece of plywood and wire it up that way instead of getting the packaged zone control.

@jmulla: I think the conversation drifted off a bit from your initial topic of two driving transformers (driving meaning operating thermostats and transformers) to how the end switch closes the leg of the boiler transformer to turn the boiler on.

This is what my Taco diagram shows. However, both diagrams show two legs of the transformer.

@jmulla,

When it come to wiring it seems neatness and aesthetics is an Art, not all Installers, Technicians, Electricians, etc. possess that talent or if they do they don't have the time and / or other resources to bother, bottom line, it just needs to work.

A nice neat job does benefit the next guy (who may be the original installer) that needs to figure it out and make a repair.

As far a paralleling transformers in your case, I would not. Yes, it would work if done correctly, but consider this.

40 VA transformers are almost as common as dirt and they match up with the load of a 3 zone valve system for a nice 'Modular' cost effective package. When installing larger systems, say 7 zones or greater you want to stay within the Class 2 wiring criteria (100 VA or less I believe). So go modular, it's easy.

Also consider the other picture on page 3 of the attached PDF above, your "Current System" is wired the same (electrically speaking), just cover up the Left two optional zones. However your system may have more wire nuts and yet it still works.



Additionally if you parallel the transformers, if TRANS 1 fails (for any reason) it may take out TRANS 2 also, leaving you with no heat. Also if there is an over-current type defect out in the system it will probably burn up both transformers instead of just one transformer.

If you stick with the modular approach and TRANS 1 fails your Master Bedroom will stay toasty warm. Also you could swap transformers to warm the rest of the house if you know the transformer's failure was not caused by a defect out in the rest of that part of the system (you would have one good transformer for troubleshooting purposes too).

Also to minimize confusion the boiler probably has its own transformer (or a third transformer).

If you want to neaten up your system and make it more aesthetically pleasing and probably easier to troubleshoot by all means go for it, however I would not parallel the transformers.

If it was my system I probably would have 2 zones on each transformer, to heat the house more evenly in the event of a single transformer failure.

HVACNUT said:

@jmulla, why not just use one 75 va transformer with a circuit breaker?

You could, and it would probably work (since there are presently only 4 zones in this case). And a properly rated and placed circuit breaker is a good idea.
However 40VA + 40VA is not 75VA and 40VA with three zones is already pushing it (0.9 A for each zone valve). If I had to use one transformer, I would use a 92 VA or a 96 VA (for 6 zone compatibility), BUT the cost !!! Two 40 VA units is much cheaper. And I believe @jmulla already has the two 40 VA transformers and wants to add a power hungry thermostat. So, if needed, he could add another 40 VA transformer for little cost to power the power hungry thermostat.

HVACNUT said:

And the Honeywell brochure diagram.

"Honeywell" I'm assuming that is a typo.

HVACNUT said:

And the Honeywell brochure diagram doesn't seem right to me. Terminal 1 is common (ground).

Terminal 1 on the Zone Valve internally goes only to one side of the heater that is around the wax filled element (not 'common' and no 'ground'). So Terminal 1 is only connected the the Independent transformer through the thermostat switch(s) and that side of the transformer is floating (not connected to anything except the thermostat(s)).

Again, in this case, for multiple reasons mentioned above by @Steamhead and myself I would have two zones per transformer which may leave enough transformer capacity for the power hungry thermostat.
A six zone controller would also work if you want to pay for it.

jmulla said: Any last suggestions?

Yes, this.

HVACNUT said:

@jmulla, When 2 and 3 close, it looks like a direct short to the Independent transformer. Or am I not looking at it right?

@HVACNUT I now see what you mean, and I agree, I was looking at the other drawing. See the Red circle below, I think it should be the coil of the "Boiler Control (Circulator Relay)" not the N/O contact shown as closed.

@EdTheHeaterMan said: Does the Nest thermostat really know what the zone valve is doing, i.e. on-off-on-off.......I don't think so.

Our modular, patented appliance is by definition virtually pre-built. The Supply Assembly Zone Sentries are pre-harnessed into 4-wire cable drop that attach to the E-Switch Control Box. Just drop the T-Stat Wires and 3-Wire Power to complete an install.
Note that by compacting & orienting the Zone Sentry LEDs negates the need for a Switching Relay entirely. The LED Status Indicators are "smarter" than a Relay, so haven't used one in well over a decade .....

@EdTheHeaterMan The Nest t-stats are compatible with our 570 series, ZVC & SR controls. Attach is a wiring diagram showing how to wire Nest to our controls and to 570 series zone valve. The only issue you will have is with more than 2 Nest to our SR controls. More than two Nest you will need to wire in an external transformer because of the VA draw on the Nest. Our 1000ohm 1/2watt resistor will not work with Nest T-stats. Nest suggests you use a 220ohm, up to 5watt resistor if needed. Any questions please contact Taco Tech Support during normal business hours Mon-Fri 8am-5pm EST. Hope this helps.

If you are going to all this trouble why not purchases some terminal strips from your local electrical supply and rewire to those strips makes for a much neater job and also easier to troubleshoot when problems arise. We need to hear from Alex the wiring nut!!!