Transistor on taco zone valve head.

BDRaff · February 1

Hello

I am replacing this taco zone valve head and the previous contractor installed what I believe is called a transistor. Why would they do this?

Intplm. · February 1

In my experience, A thermostat company needed this to allow for the related thermostat to work. This happened on my house that I owned back in the early nineties. I do not remember why the relationship between the t-stat and zone valve didn't work until I installed this so called transistor.After installing it, the zone valve worked.

I also do not remember the thermostat company. But, thats why I needed to install it and I'm thinking you have the same situation.

If you can please post a picture of the thermostat on this zone? Is it on all of the zone valves? Are the thermostats/zone valves all the same?

EdTheHeaterMan · February 1

The Taco 570 series motor has a unique internal wiring design that causes the circuit from the transformer to the thermostat to the heater in the heat motor back to the transformer to open and close several times a minute during the call for heat. (look at short answer below)

Screenshot 2025-02-01 at 10.41.18 AM.png

This is because the wax in the hydraulic piston chamber that expands to open the valve and closes the end switch does not overheat and expand past the cylinder. There is a heat motor switch that opens to stop the heater so the wax stops expanding and starts to contract. When the piston closes slightly the switch closes and the heater is activated and the wax expands. This on/off/on/off action will sometimes cause an error message to be generated to smart thermostats that reads “loss of power”. On less sophisticated thermostats the same problem occurs (but no error message is available) and the thermostat just stops working after the first time the circuit opens (which is usually within the first 2 minutes of the call for heat). The fix for that problem is to use the resistor to complete the circuit between #1 and #2 terminal on the zone valve with a small enough amount of resistance to fool the thermostat to “see” a completed circuit. But not cause any problem with the zone valve operation.

Short answer: to solve a problem with some digital thermostats

Jamie Hall · February 1

That's not a transistor. It's a resistor, and it is a kludge which is sometimes used to make a digital thermostat such as a Nest or Ecobee work on a two wire circuit. Sort of. If it is still good, and you are replacing the valve like for like, just transfer it to the new valve. If it isn't still good (and there's no reason it shouldn't be) you may be able to clean it off and read the markings and colour code on it and get a similar replacement.

You don't need it at all if you are using a battery powered or conventional thermostat.

EdTheHeaterMan · February 2

https://forum.heatinghelp.com/discussion/comment/1839519#Comment_1839519

Don't start with the difference between Trans and REsistors Jamie. Just don't go there!

mattmia2 · February 2

that's about a 2w resistor

DCContrarian · February 2

If you want to replace it with a shiny new one:

https://www.supplyhouse.com/Taco-SRTR-001RP-Optional-Power-Stealing-Thermostat-Resistor-Pack-of-6

mattmia2 · February 2

those resistors are about 40 cents each.

Joe Mattiello · February 3

the resister to allow a trickle voltage to keep power robing thermostat illuminated and working properly. The Taco heat motor valves inherently turn 24 volts on and off not to overheat the valve, and interrupts voltage to stat. Might consider adding a ZVC control?

Contact Taco tech support at 401-942-8000 for additional support. Hopefully this was helpful

BDRaff · February 11

https://forum.heatinghelp.com/discussion/comment/1839487#Comment_1839487

first, thank you for your response. the customer has 2 zone valves. this is the only zone valve with what another commenter called a capacitor. customers thermostat were just basic Honeywell thermostats, not smart thermostats. I replace both zone valves and reinstalled the capacitor. the heat seems to be working fine since i replaced both zone valves.

Jamie Hall · February 12

It's NOT a capacitor, dang it. Nor is it a transistor. Words matter.

Transistor on taco zone valve head.

Comments

Categories