C-wire for thermostat from Lochinvar

Pad_Kra_Pow

I had a lovely Lochinvar Noble installed in '19, with a simple thermostat. I just purchased a Honeywell smart thermostat. There is a blue wire which was wrapped around the thermostat wires in the house and around the wires into the Taco Valve Sentry, which I'm guessing is the unused C-wire.
However, I'm unsure where to attach things to get my new thermostat going.
Blue and red are both plugged into 18 on the boiler itself.
Can anyone assist?

HVACNUT

Can you post a wider shot of the circuit board? Preferably with the transformer. Can you see a rating for the transformer?
It seems the boiler transformer is powering zone valves, and providing power to the boiler. Unless its a 40 va or better transformer, that's not a great idea.
Typically, a system using zone valves will have a dedicated transformer (or transformers) for the zone valves and thermostats, and the end switch (blue and green wires) is part of the boiler low volt circuit. 
On the zone valve, W (red wire) is 24 volts, and C (white wire) is Common. But I would make sure you're not overloading the boilers transformer. 

HomerJSmith

Well, it all depends upon whether the thermostat connection, at the thermostat, has at least 3 conductors in the cable. As you stated, the unused blue wire from the thermostat to the Taco ZV can be used for the C wire, if so.

Looking at your pic of the Taco ZV, where does the brown colored cable go and where does the white colored cable go, and why does the Lochinvar control board have two wires in 17 & 18 slots? You have 2 thermostats and 2 ZVs?

If you have an extra unused blue wire at the thermostat, then connect that wire to the C connector on the Honeywell thermostat and the other end of that blue wire would connect to the common on the Lochinvar transformer. That may be difficult to do, besides which there are a lot of other things running on that transformer.

It might be a better strategy to employ a separate transformer and relay.

Alan (California Radiant) Forbes

On the circuit board diagram, one side of the transformer is grounded. Is this the “C” terminal and if so, couldn’t you just attach the thermostat to ground?

HVACNUT

HomerJSmith said:

Well, it all depends upon whether the thermostat connection, at the thermostat, has at least 3 conductors in the cable. As you stated, the unused blue wire from the thermostat to the Taco ZV can be used for the C wire, if so. Looking at your pic of the Taco ZV, where does the brown colored cable go and where does the white colored cable go, and why does the Lochinvar control board have two wires in 17 & 18 slots? You have 2 thermostats and 2 ZVs? If you have an extra unused blue wire at the thermostat, then connect that wire to the C connector on the Honeywell thermostat and the other end of that blue wire would connect to the common on the Lochinvar transformer. That may be difficult to do, besides which there are a lot of other things running on that transformer. It might be a better strategy to employ a separate transformer and relay.

Where do you see a ZVC panel?

HomerJSmith

Where do you see a ZVC panel?

What does a ZVC panel have to do with the price of beans? You don't need a ZVC panel to operate multiple zone valves with individual thermostats. It just makes it easier.

The question that I had is why slot 17 & 18 on the Lochinvar board have each 2 wires in them. Why does the thermostat connection on that board have 2 wires in each slot? I think that's important and provides some information on how the sys operates.

Alan (California Radiant) Forbes

There are probably two zone valves. 

Pad_Kra_Pow

There's only the one Taco Zone Sentry and only one zone for the whole house (it's quite small).
Brown cable goes to the thermostat/heater for the garage; white cable in the boiler goes to the Zone Sentry and then to the thermostat inside the house.

HomerJSmith

Pad_Kra_Pow, Good to know, Why 2 wires? Where do the cables go that connect to the ZV? The transformer on the Lochinvar is there to operate relays and other functions on the boiler and may not have enough power to run a wifi thermostat, too, which is why I would use a separate transformer and relay to run the thermostat. A inexpensive and simple fan control center would do it without compromising the Lochinvar.
https://www.supplyhouse.com/Packard-FC90113-Fan-Control-Center-120-VAC-Primary-24-VAC-Secondary-SPDT-Relay

Alan (California Radiant) Forbes

OK, can you make a sketch of where all the wires go?

HomerJSmith

I can!!! Will do it later as I must go. It would help if my questions are answered.

Pad_Kra_Pow

HomerJSmith and HVACNUT, thank you both for your time.
I think it's pretty clear that this little project (even if simple) is beyond my skillset and I'll need to call my HVAC guy; I just wanted to see if it was a matter of "Plug the blue wire into slot Z" or something.
Thanks again.