Upgrading thermostats and cables with c-wires, L8148J two zones c-wire question :)

ethan22 · June 9

Hi all! really thankful for this site as i have learned alot here over past few days!

Ok so I have a L8148J Honeywell aquastat (See images)

which was connected by previous owner in a pretty convoluted way (at least seems to me it was ) to 2 separate old Honeywell thermostats (one for 1st level and one for 2nd level of the house).

I am now upgrading my old thermostats to the ST55 Sensi Smart which requires c-wire.
Because of that I removed the old cables and ran 2 new cables (5 wires including a blue c-wire) from the old thermostat locations (1+2 floors) all the way to the utility room where I have my Aquastat L8148J. The issue is that down in the utility room the whole operations seems a mess :) see image with annotations:

im trying to figure out 2 things:

where on the L8148J so i actually have a c-wire port
since there seems to be multiple splits of the white and red cables where do i connect the 2 new cables from the ST55 (ie exactly the same as before?)

thx alot in advance, really appriciate it!

best

Ethan

HomerJSmith · June 9

Wire it this way. You have Taco 570 type zone valves. Don't expect to wire a third wire to the Honeywell. You need an aux transformer. This is for a Nest but should work for you. The TT Boiler connect is to the boiler aquastat TV & T connections.

https://www.supplyhouse.com/Jard-92290-SPST-24V-General-Purpose-Switching-Relay?_br_psugg_q=electrical+switching+relays

https://www.supplyhouse.com/White-Rodgers-90-T40M1-Transformer-40VA-60-Hz-120V-Primary-24V-Secondary-Multi-Mount

HomerJSmith · June 9

Ethan is my favorite name for a boy.

The 2 & 3 connections on the Taco ZV are just a switch that connects to the TV & T connections on the Honeywell aquastat and energizes the relay on the aquastat which turns on the pump and the gas valve's safety circuit, opening the gas valve. It's a single throw—double pole relay. You generally don't have enough power to run everything off the aquastat transformer which is why you need an aux transformer to run Taco 570 ZVs and charging thermostats. You do seem to have an aux transformer. Disconnect all the wires and rewire. Follow the wiring diagram. The diagram shows where the circuit connections go but you can make these connections in different ways. For instance, the two C wires from the thermostats can connect together then a wire can go to the #2 screw on the ZVs.

You need the relays tho. Double check your work before powering up.

ethan22 · June 10

thx @HomerJSmith!

i must say im not an expert (just a DIYer) so ill try to follow along :)

You need the relays tho

you mean i need to buy 2 relays?

thx alot

HomerJSmith · June 10

Yes, two relays. See my link to SupplyHouse.com

Just connect one wire at a time and make sure it is correctly wired.

ethan22 · June 28

thx again @HomerJSmith !

finally have time to go back to the project, since shipping at supplyhouse make things a bit pricy is this an equal relay:

https://www.amazon.com/Supco-90370-General-Purpose-Contacts/dp/B004XS148C/ref%3Dsr_1_3?crid=3T7DO04YBEFBE&dib=eyJ2IjoiMSJ9.yOnRP3yOOwh_t9uc0z2vHu6-mfI2fwrqbcyBeHWCPc3UrnuIMKk1p94C-eJSNwFqBJ4moEVFck1LMLGEmOjrrTJzSXSmimDgHkCpvyEo5usBjENOVMjAKTaH0XNT3IyLsJYe3IIrW-VAjTrrTZ6MQAuugmTT7pGL2P2cB55cBrmnxWxnuhvWdRWQln3jubX-qkaiFnl3_5tpoEdExvA5d7THBNJowtOQSyIioYIQ7BI.OfH8ZMeGCa8mR6V3ZusOW3HV4ypn3PWB18JD1y-mIog&dib_tag=se&keywords=SPST%2B24V%2BGeneral%2BPurpose%2BSwitching%2BRelay&qid=1719578459&sprefix=spst%2B24v%2Bgeneral%2Bpurpose%2Bswitching%2Brelay%2Caps%2C86&sr=8-3&th=1

thx so much again!

Steamhead · June 28

This diagram is not quite complete.

The problem is that the Taco zone valves are sending 24V out to the TT boiler terminals. The boiler control (L8148J on this one) puts 24V on one side of TT, as it is expecting a switch (thermostat) there, without any voltage input. If you get the red and white wires crossed on TT, you'll blow the zone valve transformer as well as the one inside the L8148J. Ask me how I know that……………

To sidestep this, you'll need a third isolation relay. Wire the coil terminals to the red and white going to TT on the diagram, and the normally open contacts to TT. This isolates the two transformers from each other.

Any time we encounter these 3-wire zone valves, we upgrade the job this way. It prevents future problems.

HomerJSmith · June 28

Yes, you need a relay for each thermostat. Just use the normally/open terminals and forget the normally/closed terminals.

Steamhead · June 28

https://forum.heatinghelp.com/discussion/comment/1804981#Comment_1804981

That will work. Terminals 1 and 3 are the coil. Terminals 2 and 4 are the normally open ones.

ethan22 · June 30

thx both @Steamhead and @HomerJSmith !

really appreciate your help here! got to say i will need to dive deeper into this as i must admit im a bit confused at this stage :D

can i bother your both to check if the amazon relay i posted is compatible as a relay in this setup?

https://www.amazon.com/Supco-90370-General-Purpose-Contacts/dp/B004XS148C/ref%3Dsr_1_3?crid=3T7DO04YBEFBE&dib=eyJ2IjoiMSJ9.yOnRP3yOOwh_t9uc0z2vHu6-mfI2fwrqbcyBeHWCPc3UrnuIMKk1p94C-eJSNwFqBJ4moEVFck1LMLGEmOjrrTJzSXSmimDgHkCpvyEo5usBjENOVMjAKTaH0XNT3IyLsJYe3IIrW-VAjTrrTZ6MQAuugmTT7pGL2P2cB55cBrmnxWxnuhvWdRWQln3jubX-qkaiFnl3_5tpoEdExvA5d7THBNJowtOQSyIioYIQ7BI.OfH8ZMeGCa8mR6V3ZusOW3HV4ypn3PWB18JD1y-mIog&dib_tag=se&keywords=SPST%2B24V%2BGeneral%2BPurpose%2BSwitching%2BRelay&qid=1719578459&sprefix=spst%2B24v%2Bgeneral%2Bpurpose%2Bswitching%2Brelay%2Caps%2C86&sr=8-3&th=1

i will perhaps create a diagram in a few days and post it here before it try to actually do anything :D

thx again so much

Ethan

HomerJSmith · June 30

Yes, again. Just use the normally open terminals.

Alan (California Radiant) Forbes · June 30

Why go through this torture when you can purchase a Caleffi or Taco control that gives you your "C" wire and has a landing spot for every other wire you have AND has diagnostic lights to help you when there are problems?

Not shown is a pair of wires from "XX" on the control to "T" and "TV" on the Honeywell aquastat as your end switch.

Controllers are available in 3,4,5 and 6-zone configurations.

Screen Shot 2024-06-30 at 11.41.59 AM.png

HomerJSmith · June 30

@Alan, comparably it cost big Buckos. No, for those of you in Rio Linda, a Bucko isn't a wild animal in Australia.

ethan22 · July 1

thx both! @Alan (California Radiant) Forbes , since i am not a professional i would be wiling (within reason :)) to pay some more for a much more simplified approach (will probably costs way less then a technician right).

Can you perhps link to the Caleffi or Taco controler? googling didnt really point me in the right direction :)

also (if possible) can you explain in detail what connects where with such a controlor?

i really really appreciate all you guys time, its such a great community here!

Ethan

Alan (California Radiant) Forbes · July 1

https://www.supplyhouse.com/Caleffi-ZVR103-3-Zone-Valve-Control-w-Priority

https://www.supplyhouse.com/Taco-ZVC404-4-4-Zone-Valve-Control-Module-with-Priority

There are links to the installation instructions. Read them and let us know if you have any questions.

SteveSan · July 1

@ethan22 If you do end up going with the Taco ZVC control, please give Taco Technical Services a call during normal business hours Mon-Fri 8am-5pm EST 401-942-8000 and just ask for Technical Services.

ethan22 · September 4

Hi guys and @Alan (California Radiant) Forbes !

So kids are back to school and im finally back to the project (have to do it before the winter:))

i bought the Taco ZVC control the you recommended (ZVC404-4) and now trying to get back to things and try to figure out how to actually wire this

ive drafted a diagram to myself but i am at a bit of a loss here as not everything is clear to me

you mentioned there are a "wires from "XX" on the control to "T" and "TV" on the Honeywell aquastat as your end switch" which i drew up as gold and blue lines in the diagram above. but currently there "TV" and "T" sockets are connected to the first Taco 671-2 zone valve :

so i guess im still confused on how to connect the ZVC404 to the main aquastat and the actual taco zone valves :)

any help would be super appreciated :)

thx so much

Z

Steamhead · September 4

X-X on the ZVC goes to TV-T on the aquastat relay.

The zone valve terminals 1-2-3 go to 1-2-3 on the ZVC for the zone they serve.

ethan22 · September 4

amazing @Steamhead ! really appreciate it. i have updated the diagram, did i plot it correctly?

to confirm ,currently the taco zone valves are connected to each other in the new setup they are just connected to the ZVC right?

Steamhead · September 4

https://forum.heatinghelp.com/discussion/comment/1809446#Comment_1809446

Yes. Run a 3-wire cable from each zone valve to the proper 1-2-3 terminals on the ZVC. Do not connect the zone valves together.

ethan22 · September 4

thx so much again, last question (i hope :))

Run a 3-wire cable from each zone valve to the proper 1-2-3 terminals on the ZVC

so i need a white,red,green cable, but how does one know on the zone valve itself where it goes? (or is there no order needed)?

thx so much to eveybody in the wonderful community!

Steamhead · September 4

Wire 1 to 1, 2 to 2, 3 to 3. Doesn't matter which color goes with which number as long as they are the same on both ends.

ethan22 · September 25

Hi all

im just updating that everything was installed and works well!!

i want to thank every single person here, i cant thank you guys enough

if everything in the world worked like this community we would live in an utopia :) :)

thx again!

Z

Upgrading thermostats and cables with c-wires, L8148J two zones c-wire question :)

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