Taco Zone Valve Controllers ZVC series and the end switch - interesting note

scraphound

One of the things I do for my job is help people located in remote isolated Arctic villages fix their heating systems over the phone. I was walking a guy through replacing his Taco ZVC series zone valve control yesterday. They've been failing recently, but that's a different story. The new one was a different model than the old one, but eventually we got it wired up properly and working (btw... if the Taco is getting power... green light on.. but it's not sending power to the zone valve (not turning the green zone light on) then check the fuses. You can't tell if they're good by looking at them... check with a multimeter). Unfortunately, after we got the Taco working we discovered the end switch wasn't making contact on a brand new honeywell 40003916 zone valve... the circ-pump wasn't turning on. You can fix the Honeywell zone valve with a pair of needle nose pliers (also another story) but I dreaded explaining how to do it over the phone. I ended up telling him to disconnect the red honeywell end switch wires from the taco board and installing a jumper wire between terminals 3 and 4 (the zone valve was rotating open/closed just fine). I did some testing before I told him to do this. What I discovered may be of interest to others.
For those who are still learning, the end switch is a safety device designed to not turn the circulation pump on until the zone valve has rotated to the fully open position. When the zone valve motor receives power it physically rotates a valve and presses a switch. When somebody cranks hard on the zone valve's manual actuator lever the gutts get bent inside and the end switch stops making contact (a source of major frustration over the years). I was tempted to have him jumper terminals 3 and 4 on the Taco board to bypass the zone valve end switch, but I was worried that if he did this the circulation pump would run all the time.
I checked it out and discovered that the Taco engineers had though of this.
What I discovered: If you jumper terminals 3 and 4 (the end switch terminals) on the Taco board it DOES NOT turn the circ pump on (great!). Both a call for heat from the thermostat and a closed end switch are required to actuate the circ pump. It even has a built in delay after the call for heat (giving the zone valve time to rotate). So instead of trying to explain to this guy how to look into the side of his Honeywell zone valve and twist its legs with a needle-nose to get the end switch working, all I had to do is tell him to jumper terminals 3 and 4 on the Taco zone valve controller. Figuring out that this was ok to do and would work took a bit of testing, so I thought I'd pass it on to the world!...Stay safe. Stay healthy. Stay warm!

STEVEusaPA

If the end switch doesn’t make, and the valve doesn’t open, you have to manually open the valve, otherwise you’ll deadhead the circulator. Jumping 2&3 makes the boiler run forever.
The end switch isn’t classified as a safety device.
What exactly are you muttering on about?

HVACNUT

Yeah that post was an answer without a question.
No secrets there.

STEVEusaPA

OP, if you have these remote repairs to walk people thru, make videos, charge them for access, or video chat with them.
I see this going the way of many customer service. Facetime, zoom, video chat. Collect a fee, virtually no overhead.
Sounds enterprisingly interesting to me.

Joe Mattiello

Hi Scraphound
ZVC control R W terminals need to close in order for zonevalve to open, zone valve endswitch to close through 3, and 4 terminals to close main endswitch to fire boiler TT terminals. that's protocol. The honeywell 40003916 zone valve may require 24 volts to close the switch for a demand. to prove that out, you can jump R W, on the ZVC to see if the zonevalve opens.
as you mentioned terminals 3, 4 has to see endswitch closure to pull in main endswitch, sort of protection against perpetual call. for example, if zonevalve stays open boiler will continue running. It's not uncommon to have a 2 terminal zonevalve without and endswitch, so jumping 3, and 4 on ZVC will work, just be cognizant of potential perpetual demand if zonevalve malfunctions.
The LED lights provide diagnostic tools too. Green light means you have power, as mentioned. It’s an easy control to work with, and pretty straight forward.
Hopefully this was helpful, and if anyone has additional questions or concerns, contact Taco Tech support at 401-942-8000 and ask for Tech support.

hot_rod

And consider Caleffi Z One zone valves. The end switch is a reed type and closed by a magnet in the gear. No more “rubbing” the microswitch open.
The reed switch also handles digital signals better than “vending machine” switches😉

HomerJSmith

Remote Arctic villages are more than not run on a village generator. It is possible that the Total Harmonic Distortion (THD) and spikes may be high with some of these generators. A 115V isolation transformer is sometime needed or a line conditioner.

Might help with premature failure. In some of the early Munchkin installation had problems because of dirty sine waves which a line conditioner fixed.

BDR529

Zone valves in the Arctic, Brave man!

HVACNUT

> @BDR529 said:
> Zone valves in the Arctic, Brave man!


How so?

hot_rod

Normally open zone valves are sometimes used in applications where the power could go out frequantly. They can allow some gravity circulation.

BDR529

Really...
Arctic is very cold. Lets do a single pump,micro switches, add'l step down transformer with spaghetti wiring. Lets add in a generator with a bad sine wave as well.

With those temps, pumps, relays and checks. Done simple.

HVACNUT

> @BDR529 said:
> Really...
> Arctic is very cold. Lets do a single pump,micro switches, add'l step down transformer with spaghetti wiring. Lets add in a generator with a bad sine wave as well.
>
> With those temps, pumps, relays and checks. Done simple.


It's not simple for someone who never worked in artic temperatures. That's why I asked. I didn't rebut.