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Replacing my Taco 568-14

whiplash68 Member Posts: 2
edited September 2022 in THE MAIN WALL
Hello all!

I am hoping for some advise to change out my old Taco 568-14 thermostat to a digital programmable unit. System is heat only. Oil fired burner/boiler. 3 zones in our house that are baseboard radiated water piping. Each zone has a 3 wire Taco valve.

Would like to replace with a digital programmable thermostat. Researched and think a Honeywell RTH6360D1002 may be the answer. I am confused though about line voltage. How do I know what the voltage is...short of disconnecting the wiring and forcing the heat System to call for heat and measuring voltage on each of the 2 wires coming out of my wall?

I just checked, and the solenoid valves are 3 wire, manufactured by Taco. There seems to be a model number part of the body casting that says 571-2. After researching, I did not realize how much technology is built into it with the end switch and how it is wired into the System with the thermostat and boiler/circulator (pump) controls.

Thank you all.


    EBEBRATT-Ed Member Posts: 15,710
    Those valves are 24 volt
    HVACNUT Member Posts: 5,870
    That thermostat is fine. You'll need to use the batteries. 
  • 109A_5
    109A_5 Member Posts: 1,387

    I am confused though about line voltage.

    Line Voltage usually refers to 120/240 VAC often found with Electric Base board heating.
    With a Taco 571-2 zone valve your system is most likley 24 VAC. There should be a transformer in the vicinity of the boiler that reduces the 120 VAC to 24 VAC for the Thermostats control Voltage.

    National - U.S. Gas Boiler 45+ Years Old
    Steam 300 SQ. FT. - EDR 347
    One Pipe System
  • whiplash68
    whiplash68 Member Posts: 2
    Thanks for the comments. I didn't realize it is probably 24vac. I figured DC. Think when I feel ambitious I will look at the control box. Youtube vids + my Engineering curiosity makes me want to close the loop on learning how my System works.
  • Joe Mattiello
    Joe Mattiello Member Posts: 707
    Hi Whiplash
    Is you want to go with a setback type thermostat to save energy, that’s fine. No additional wiring required, providing you select a battery operated thermostat. Those 3 terminal heat motor type zone valves are really cool. 
    I’ve always been impressed with engineering doubling up on terminal 2 as twofold thermostat and end switch to energize the boiler on demand.
    setback is great providing your schedule is regimented. 
    I personally have radiant heat and run my system continuously at 72 degrees. I use boiler reset which Taco offers a control to do that. Keep in mind your window of opportunity to rest the boiler is between 140, and 180 degrees if you have a non condensing boiler. Sorry, if I’ve over complicated things, but you can look at it, as one size does not fit all:-)
    I suggest you call those fine folks at Taco, 401-942-8000, ask for tech support, and they’ll be happy to provide a little direction. 
    Hope this was helpful, and have a blessed day! 
    Joe Mattiello
    N. E. Regional Manger, Commercial Products
    Taco Comfort Solutions
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 8,153
    edited September 2022
    This booklet will help you understand the wet side of the system.

    The electrical side of that zone valve you have is quite interesting. Here is a diagram of all the internal parts. You can see how the heater at the top connected to terminal 1 & 2 will take the 24 VAC and cause the wax inside the piston to expand from the heat. The hydraulic pressure of the expanding wax then forces the valve open and also moves the cam to operate 2 micro switches. As the cam moves, the first switch to close is the end switch that is connected to terminal 2 & 3. This can be used to do what a thermostat might do on a single zone system. Connect to the boiler control the operate the burners, circulator, and/or any other needed operation.
    The cam continues to move and operate the second normally closed micro switch that breaks the heater circuit so the wax does not build up excessive pressure and force the wax to break the seal on the piston. Once the heater is off, the wax will cool and the cam will retract and the heater switch will re-engage and cause the wax to expand. this cycle continues until the call for heat is satisfied.

    Edward Young Retired

    After you make that expensive repair and you still have the same problem, What will you check next?