Taco ZVC control with ESP zone valves

Alan (California Radiant) Forbes

I replaced a Taco ZVC control this week because the end switches weren't closing; both the boiler and pump didn't come on; very rare. The new ZVC worked fine for a day and then did the same thing: no end switch closure on either switch. The ZVC showed the yellow and red lights on both zones when there was a call for heat.

I switched one of the operators to a Zone Sentry operator and bingo: pump and boiler came on. That's a first for me. And a coincidence that both operators had the same symptom.

HomerJSmith

Alan, those ZVs are series 1 ESP. Series 1 was problematic. 2002 manufacture date. Series 2 looses the charge, too. I replaced all those with Sentry ZVs. They just snap on the old brass valves. I never had to replaced the zone valve controller.

Alan (California Radiant) Forbes

Yes, I've had problems with them, too. But they were different problems. Sometimes the valve was bad and it became too hard for the operator to open and close; you had to replace the entire valve. And sometimes there were issues with the operator. But I've never seen an operator close an end switch after opening, telling the control that the valve is open and the end switch is closed with the red light on the control turning on, acknowledging that the zone was ready for the boiler and pump to come on, but the dry contacts on the ZVC remain open.

The old control was probably fine and I didn't need to replace it.

HomerJSmith

I see your point.

Joe Mattiello

Hi Alan
Those are the original electronic ESP series zonevalve. I'm glad to see they have been working for you for approximately 20 years. there were some issues with them, and as taco continued to address those first generation of valve issues, they introduced the Zone Sentry which has been bullet proof. I personally have 13 of them in my own home radiant system; I'll try to post a picture
As for your specific issue, it makes sense the control endswitch wasn't closing because the zonevalve endswitch might have gone bad. at the bottom of the control terminals 1234, 12 is 24volts out to power open the valve, and terminals 3,4 are basically communication terminal inputs acknowledging valve endswitch closure, and valve opening. It was designed this way to minimize a perpetual demand if the boiler fires and the valve doesn't open. for diagnostic purposes you can jump out 3, 4 terminals to simulate valve endswitch closure to prove out the control. I believe we show a jumper across those two terminals to accommodate a 2-terminal valve with no endswitch. Hopefully this was helpful. BTW, the valve exceeded its warranty period by about 16 years; lol
Please try the Taco Zone Sentry valves they are awesome.

Alan (California Radiant) Forbes

Dave & Joe at Taco: Thanks for chiming in! It's great to see you taking the time to support Taco products and it means a great deal to me.

When the ESP zone valves first came out, we were all in and used them on every job only to see many start to fail. Some lasted a few months, others are still around now. Thank goodness for the replacement Zone Sentry series that snaps onto the same body and is much quieter.

But it doesn't seem as though I'm getting through to anyone (except Homer) the point that:

How does the zone valve end switch close and the zone valve control acknowledge closure by the red end switch light coming on without the dry contacts closing? And when I replaced the zone valve, everything worked. The end switch is either open or closed, no?

I'll crack open one of the old zone valves to see if I can get a clue.

rick in Alaska

"How does the zone valve end switch close and the zone valve control acknowledge closure by the red end switch light coming on without the dry contacts closing? And when I replaced the zone valve, everything worked. The end switch is either open or closed, no?"

I understand what you are asking. Maybe the end switch was barely closing and sending a weak signal to the zvc, enough to make the light come on , but not enough to make the zvc end switch close?? It doesn't seem right, but I haven't looked at the control enough to figure it out.
Rick

hot_rod

What type of thermostats are you using? Have they changed?

Alan (California Radiant) Forbes

@rick in Alaska Yes, that's the way I'm thinking as well.

@hot_rod Same tekmar stats.

rick in Alaska

Are you using the resistors in the zvc box with those Tekmars? It might make a difference.
Rick

Alan (California Radiant) Forbes

No, the tekmar thermostats were powered by a separate transformer.

Alan (California Radiant) Forbes

My son took the zone valve apart and found the culprit:

"The contact in the micro switch wore out or had too large a current/voltage applied. In traditional failure analysis lingo, it experienced an EOS (electrical over stress). The arrow is pointing to the movable contact point, and the circled portion is the stationary point (normally open).

As fas as the light on the control showing zone valve closure without the dry contacts closing:
"When I checked it with a meter, the contacts weren't closing at all. It's possible something snuck through with 24VAC applied."