Extra zone coming on with priority DHW

wt

Hi all, I'm not sure if our Taco ZVC 406 is fritzing out or what. Whenever our DHW (zone 6, priority on) calls, our zone 4 comes on. The box is 19 years-old but nothing has changed with it in terms or wiring or anyone doing anything with it or to it. I just happened to notice both zones on one warm day, so I tested it and sure enough, zone 4 calls whenever zone 6 calls. It appears as if zone 6 is causing zone 4 to call. Anyone ever seen something like this? Do I need to get a new Taco unit?

Thank you very much in advance,

Will

wt

No ideas yet? I'm a little surprised. Should I just replace the ZVC 406 and cross my fingers then?

Thanks

Paul48

I'd say replace it. It's doing something, it should never do.

HVACNUT

If you remove wires from TT on zone 4 and jump TT on zone 6 and zone 4 valve still opens, it's internal and you need a new board.

Dave H_2

Start with the simple "testing" like @HVACNUT suggested. Each circuit should be separate.
Isolate each zone and test one at a time.

Dave H

wt

Indeed - I jumped zone 4 TT to 6 TT and it again caused it to call. Will replace board. Thank you!