Tekmar thermostat 518

chippy2 · 2:32PM

hi I am using a couple of Tekmar 518 thermostats with floor sensors for my radiant zones. Have a Taco ZVC504-5 and Caleffi 4 wire actuators. Even though the ZVC504 shows numerous Tstats using only R/W wires, my thermostats aren’t live and would appear to need a separate 24v supply? Is that true and can I tap 24 off the ZVC ?

SteveSan · 3:41PM

Some two wire t-stats need the resistor connected to the W-C terminals. Easy way to confirm if you take away the R-W from the Taco ZVC t-stat terminals and "jump" the R-W with a jumper. If it sends the signal to the zone valve, then that confirms you need the resistors.

If you have any questions, 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

chippy2 · 4:31PM

OK thanks but are you also saying those Tekmar t-stats do not need a 24v supply to them?

Alan (California Radiant) Forbes · 4:32PM

https://forum.heatinghelp.com/discussion/comment/1903818#Comment_1903818

Hmmmm. Won’t a jump between R-W always signal the zone valve to open regardless of whether the thermostat needs a resistor or “C” wire?

Alan (California Radiant) Forbes · 4:39PM

@chippy2 Every tekmar stat I’ve seen needs power.

If your ZVC has a metal cover, Taco doesn’t give you a marked “C” terminal. You have to steal it from the unmarked transformer terminals on the board and have to figure out which one is the “C” wire.

The newer ZVC’s with a plastic cover give you a “C” terminal for every thermostat, right next to R-W.

chippy2 · 4:54PM

Thanks. Unless I’m wrong the C terminal is common and the Tekmar still requires 24v. There is a 24v tap on the Modbus connector that I can use.

chippy2 · 4:55PM

SteveSan · 5:04PM

https://forum.heatinghelp.com/discussion/comment/1903829#Comment_1903829

Alan, on the metal cover ZVC controls. See below.

-2 ZVCs Wiring

White= Left “T”

Red = Right “T”

Common = # 1 Terminal for each zone valve terminal

@chippy2 if your current t-stats do have a common, then just wire to the C terminal at the t-stat terminal on the ZVC control. Always between R-C is 24v.

AS Ed suggested, might be better if you call into Tech Support and chat with a live agent. We are here until 5pm EST.