Adding Taco ZVC404-EXP-4: Function & Wiring questions

sgnl05

Hi all - here's a quick overview. I'm a DIYer that's been reading around and trying to confirm function/wiring so I don't damage any system components. I have the 100+ page Taco wiring PDF and several of the diagrams initially look like they will work for my system. I've been overthinking things a bit so wanted to get some outside opinions. Thanks in advance for any assistance here.

——————————————————————————————
Existing System
- 1x Navien NCB-210E Combination Boiler
- 1x Taco 007-F5 Circulator
- 1x Taco SR501-4 Switching Relay
- 4x Taco Zone Sentry Zone Valve
- 4x Nest Learning Thermostat

I want to add
- 1x Taco ZVC404-EXP-4 Zone Valve Control

——————————————————————————————
NOTES
1. The existing system works fine, there are no issues. I am simply looking to tidy things up by integrating the Taco ZVC404-EXP-4 Zone Valve Control.

2. I hope to add some radiant in floor heating in the future. (Thought this could be a factor in responses.)

——————————————————————————————
SYSTEM/COMPONENT FUNCTION
The Navien NCB-210E handles all DHW operations internally so, in theory, I should only need to wire the Taco SR & ZVC units for heating. As I understand it, the SR501-4 is for operating 120V components while the ZVC404-EXP-4 will handle the low voltage components.

1. Do I need both the SR501-4 *and* the ZVC404-EXP-4? I ask because it looks like the ZVC404-EXP-4 is capable of handling the circulator on pages labelled 28 & 50 (bottom) of the Taco PDF.

2. If I keep both the SR501-4 and the ZVC404-EXP-4 in the system, pages labelled 11 & 54 look like they could they should work. Is there a benefit to one being the master over the other (switching relay vs zone valve control)?

Again, thanks in advance for any help - it's greatly appreciated.

STEVEusaPA

You most likely don't need the 501 at all.

sgnl05

STEVEusaPA said:

You most likely don't need the 501 at all.

@STEVEusaPA that's what I'm thinking. Didn't want to eliminate any components as the original system was installed by pros. Thanks for your input.

Dave H_2

What is the type of heat that you have now? Sounds like hi-temp since you have plans to add radiant.

The radiant floor system will probably need a lower temp then the existing system therefore you will need a mixing valve to bring that water temp down.

Once you add the mixing valve, you will need to add another circulator so you may need that 501 controller.

Dave H.

sgnl05

Dave H_2 said:

What is the type of heat that you have now? Sounds like hi-temp since you have plans to add radiant.

The radiant floor system will probably need a lower temp then the existing system therefore you will need a mixing valve to bring that water temp down.

Once you add the mixing valve, you will need to add another circulator so you may need that 501 controller.

Dave H.

@Dave H_2
The heating is currently hot water with baseboard units - some tube & fin, some cast. Yes, repurposing it elsewhere was my thought of hanging onto the SR501 if it would no longer be in use with the current system.

Thanks for the heads up with the radiant components. I'm just starting to look into it now. It may or may not happen this season.

EdTheHeaterMan

Nest may not work in that situation. It may find the design or the Taco 571 actuator's open circuit to the heater in the actuator as a fault. I needed to add isolation relays to Taco zone valve to correct the issue. The Taco Z075P2-2 and Honeywell zone valves do not need isolation relay.
Not sure if the ZVC relay is a true isolation relay as far as the Nest is concerned.
There is one benefit to the ZVC control. You can add a common to the NEST to make it recharge the onboard battery. Otherwise, the Nest battery only charges when there is no call for heat.

sgnl05

EdTheHeaterMan said:

Nest may not work in that situation. It may find the design or the Taco 571 actuator's open circuit to the heater in the actuator as a fault. I needed to add isolation relays to Taco zone valve to correct the issue. The Taco Z075P2-2 and Honeywell zone valves do not need isolation relay.
Not sure if the ZVC relay is a true isolation relay as far as the Nest is concerned.
There is one benefit to the ZVC control. You can add a common to the NEST to make it recharge the onboard battery. Otherwise, the Nest battery only charges when there is no call for heat.

Thanks for the info. I've read a few different solutions with Nest & Taco including isolation relays and 1k Ohm 0.5 W resistors. I'll report back once I get everything up and running.