Wiring HydroStat 3250 With Multiple Circs and ZVC

2468ben

Hi folks, I've been planning to switch my oil boiler setup to a Hydrostat and use as many perks as possible. Luckily I saw a diagram on Taco Tuesday with exactly my setup (first image). I've got two pumps, one for space heating and one for indirect, no common system pump.

I assume that there's no clever way to run the space heating pump from the hydrostat, since there's a separate pump for the DWH. If there is then I'd love to do that and get hold off. Otherwise taco suggested this setup (ignoring the orange line they drew):

Hydrostat wants an extra wire from the taco N/O to its ZR, letting it know when to override economy.

If I have to run a 120V wire between the two controls, both touching the boiler, can I run the TT/XX wires on 120V too?. I've got an extra length of 14/4 in an armored cable, and the Hydrostat TT seems like it supports 120V or 24V, so I was wondering if I could connect it with the 120V XX end switch instead of the 24V one. Then I have all 3 connections (plus ground) in one metal cable, and can skip running low-voltage wire next to all the hot stuff.

The other question about doing it that way, is I don't know what the taco ZVC's "pump exercise" function does with the end switches. I know it exercises the zone valves, but does it do anything to (N/C, N/O or X/X)? I'd love to enable the feature but wanna make sure it wouldn't cause an issue with the 120V X/X going to the hydrostat too.

Steamhead

I wouldn't run 24V in the same cable as 120V. That is never a good idea and may not meet Code. Is there an existing 120V cable between the ZVC and the HydroStat? If so, replace it with one having the extra wire.

Not sure about the exercise function, maybe one of the Taco guys will chime in here.

Robert O'Brien

You can run the heating pump on C1 terminal of 3250. XX on ZVC to TT on 3250 is 24v only. Still need 120 from DHW pump to ZR.

Line and low voltage can not run in same conduit. Low voltage can be secured to the outside of conduit carrying line voltage but only to the appliance it’s controlling

2468ben

Thanks, I wasn't planning to run 24 and 120 together, only to run 120 for all the wires if the Hydrostat TT supported it. In the Hydrostat wiring examples, a lot of the TT connections are to end switches on the bottom bars of relays + zone controllers where things look like 120V, so that's why I wasn't sure what voltages the Hydrostat TT will accept, or if the 120V Xx pump switch on the taco act any differently than the 24V XX one.

Robert O'Brien

TT is 24V only, 3250 has an integral transformer

Dave H_2

The ZVC-exp will exercise the valves as well as the circ but not the boiler or DHW endswitches.

2468ben

Thank you @Dave H_2. So with that wiring setup from the Taco screenshot, the N/C and N/O won't be exercised, or just N/C will?

2468ben

Update: I forgot to mention I had to replace my old system pump and got an Alpha 15-58, running in delta P mode. So I think the Alpha might let me do everything and "exercise" the system pump during the summer.

The Hydrostat manual says this:

Smart DHW Priority: During a call from an indirect water heater, the control will de-energize the circulator contacts (C1/C2) to
heat only the indirect tank ensuring an adequate supply of domestic hot water. The control will re-energize the circulator when
the indirect tank is satisfied or if the boiler temperature reaches 170°F. If the indirect call continues for 45 minutes, the control
will override the priority function energizing the circulator to provide space heating.

1. Wire the system (alpha) pump directly to the Hydrostat C1/C2 contacts, letting me use circulator hold off
2. Keep the DHW (fixed speed) pump wiring separate, and connect it to ZR on the Hydrostat, which will turn off C1/C2 when an indirect call happens and switch from economy to my high limit.
3. If I keep my high limit above 170, then it looks like the Hydrostat will re-enable C1/C2 at 170F, so for the couple minutes between then and the DHW call being done, the system pump will turn on. Since it's the alpha it will idly sit in delta-p with the zone valves closed for that minute or two, but I've heard that doesn't hurt the pump at all. And it means the system pump gets a tiny bit of exercise every day at the end of a DHW call

I know this is a pivot from before but it sounds it would wouldn't hurt the Alpha pump, let me have circulator hold off, and exercise the system pump without it being on 24/7?