Taco 700 Question

archibald tuttle

I think that the ZR terminal does make if the reset is calling the boiler because I am using the ZR on a 503 exp in reset mode and it is hot whenever the 700 calls the boiler. But if you are just showing boiler demand on the 700 but not a call to the boiler to fire then ZR is dead. The labeling of these two conditions is a little confusing but there is no mistaking the icons. The firing icon is obvious.

If you are just calling the pump for the boiler leg only then this might work because it will call whenever the boiler is fired. But if you want a primar loop circulator running whenever there is any circuit demand this won't do it. I have to think till the next post about how I tricked out a signal to a relay to run a main circulator whenever any zone on the 506 was calling even if the boiler was not firing. I'll get back to you.

Brian

Will_5

Taco 700 wiring

Just installed a Taco 700 & 506EXP today, I have a small control problem. I need to run a loop circ because I piped it Primary / Secondary, I see in the wiring manual it shows on a 702 & 705 diagrams to wire the system circ off of ZR & the neutral on the slave relay, I tried it of the master panel ( I don't have a slave ) and it only works in the NORMAL function, not the RESET. Do I have to get a 501EXP,run the 700 into that,turn my 506EXP into the slave and run my loop circ of off that?

I hope someone can figure out what I'm talking about!!

Singh_3

Depending how the primary pump is piped, why not run it off
the circulator terminals on the boiler.
This way when the boiler fires , the circ runs.
The drawback to this is if you have an indirect or other zone, you may not need the PP to run when those zones call,once again depends on piping .

Will_5

Can't do it

The problem with doing that is the boiler is control from XX on the 506, when the 700 reaches it's target temperature de-energizes XX and kills the call for heat to the relay, the zones circs keep running but no flow through the boiler. I have it wired constant circ for the moment, I imagine there will be a call for heat continuosly by at least one zone over the next few days!! It's gonna be quit cold.

EJW_3

Taco 700

Jimmy, you can get another Taco EXP control but I think the smallest expadable is the 503. I had to do this once.

EJW

archibald tuttle

501 exp coming??

I understood that they were going to come out with a 501 exp because I tried to buy one last year when I needed two different setback temperatures on one job, but the price difference between a PC 700 and Tekmar 256 has opened up a bit anyway so the convenience of the plug and play now comes at a greater expense.

Anyway, the 501 exp seems to be in response to this difficulty of not having a master 'end switch' that responds to zone demand and another that responds to boiler fire demand from the 700. The other thing I wanted in the 503 and 506 that they have ignored (so far) is NC contacts like they have on the 501 that I employ now and again in my heating logic experiments (admittedly, some would say illogic).

Another problem is that the priority switching on the exps cuts the 700 (or 702 or whatever) completely out of the temperature control equation. I didn't realize this when I first wired it up and I couldn't figure why my boiler was overrunning the design upper limit on the 702. Then I realized that I had no temperature regulation when the priority circuit was calling. I have come across another boiler wired this way be a plumber on another job. I knew to look for it because I had made the mistake.

Another thing i have run into is having several legs that want the priority temp and you can only have one circuit set as priority. A little priority switch under each circuit would be cute. Of course if the total logic were not addressed but simply switching legs to the priority or non side, this would result in slower DHW makeup. When I am trying to run a baseboard setback off the base exp but I need higher temp for a hydro air and DHW and ...., I tend to throw another 503 to pick up all the priority loads and put the DHW on the priority on that second 503 and then pull the priority on the primary with the xx off the slave. For complicated systems this is usually pretty cost effective but on controls like the 506 and larger it would be nice to be able to add one or two more circuits to the priority.


In any event, if they do ever come out with a 501exp I wonder if it will be significantly cheaper than the 503exp, but if you need NC contacts or something unusual it might still be worth it.

I don't know how long it takes for taco or tekmar or whoever makes this stuff to get back enough on their circuit board design to start to incorporate these anamolies into their workhorse 503s and 506s. These are great controls but they could be a lot better. Well, come to think of it, the taco zone valve heads have needed a fully independent end switch for 20 years and they've never got around to fixing that so maybe we better learn to live with what we've got.

Joe Mattiello

The SR503-EXP 3 zone capacity switching relay control will interface with the PC700-2 outdoor reset control microprocessor for outdoor reset operation. If you have primary secondary piping with a primary circulator, you cannot use the ZR terminal for a primary circulator because the PC700-2 modulates the boiler through the XX terminals. XX terminals use the same relay as ZC/ZR terminals causing ZR terminal to continuously open, and close causing the primary Circulator to stop running with the boiler. If you have primary secondary piping and you need a primary pump to run, you might consider using the PC702 2 boiler staging control which interfaces with the TT terminals on the boiler directly. See attached instruction sheet for the pc702-2