TACO ZVC-403 not calling for heat from GB142

kinderhund

Our system is setup with a Buderus GB142 boiler, that provides both HW and supplies 2 radiant heat zones.
We had a lengthy outage on the GB142 while we replaced the transformer and UBA
(https://forum.heatinghelp.com/discussion/167332/buderus-gb142-9p-error-code)

Now the HW works, but having an issue with the radiant heat. The ZVC-403 valve controller is wired to two thermostats, each controlling a separate zone, and each zone having multiple Caleffi zone valves.
When the thermostat calls for heat, the TStat light on the ZVC lights up. Good sign.
Once the valve warms up, the valve light comes on. Good sign. And the valves are warm to the touch, so its more than just the light.
The ZVC should then send a signal to the boiler (and the pumps?) via the end switch terminals. The signal to the GB142 goes into the AM10 module, then out to the boiler.
Here's where I seem to have the issue. The AM10 doesn't register that there has been a call for heat. So I tried to bypass it and connect the wire coming out of the ZVC end switch directly into the TT Connection "WA" on the boiler. Still no firing.
I should note as well that when I did this, I turned the power off to both the boiler and the ZVC (wall switch upstream of both). When I turn it all back on, the pumps run for a few minutes, and then turn off. I'm assuming that's just a priming mode or something.

So all of this leads me to believe that the ZVC is not sending a signal to the boiler.

Last piece of info, the screws on the end switch terminal have quite a bit of corrosion (see attached image). Other screws have similar corrosion (like on the TStat and valve connections). Seems like water may have gotten in there at some point).

While I try and hunt down my multimeter (how does THAT go missing?), any ideas?

STEVEusaPA

Yeah looks like water damage, or at least a lot of humidity/moisture. Enough that you should find the source.
If you remove the two wires on the end switch on the panel and twist them together the boiler should fire. If it does you should also have continuity on the end switch (switch closed). If you don’t further investigation in the zone panel is required.
If the boiler didn’t fire, go to the end switch on the aquastat/boiler control, remove the wires coming from the zone panel and jump x-x (t-t). If the boiler fires it’s in the wires.
You could first try cleaning wires/terminals on the zone control because it looks like that control is probably water damaged.

Ironman

Simply jumper the end switch terminals on the ZVC and see if the boiler fires.

Considering that it's had water on it, the ZVC should be replaced either way.

STEVEusaPA

Hey Bob, what do you think about 3 zone valves attached to 1 block on the control?

HVACNUT

Have you tried jumping WA directly?

Ironman

STEVEusaPA said:

Hey Bob, what do you think about 3 zone valves attached to 1 block on the control?

Not the greatest idea. It looks like leads from manifold actuators.

kinderhund

Update: Thanks for the suggestions guys. I tried Steve's suggestion to remove the wires from the ZVC and twist them together, with the ZVC still calling for heat to keep the valves open. The boiler fires in this scenario. So that confirms that the issue is with the ZVC.
I also agree with Bob's comment, probably time to replace given the apparent damage. We had a water leak at one point that sprayed a lot of water everywhere down there, that's likely how it got in there. For some reason, the ZVC is mounted about 4" above the floor. Not great. I'm going to find a better spot.

As for the multiple zone valves connected to the 1 block, not sure I have much choice. They're all controlled by 1 thermostat.

Ironman

Jumper them on the thermostat side terminals instead of ganging them up on the valve side. In other words, use a larger ZVC and put each actuator on separate zone terminal and jumper them at the thermostat terminals on top.

Dave H_2

Three actuators to one terminal on a ZVC is not a problem. The actuators have a very low load.
Load wise, i may max out to 4 on one terminal depending upon the draw of the actuators

Dave H