Domestic HW zone not calling for heat until another zone calls for heat

mtschneider1

I have a 4 zone system. Zone 1, 2 and 3 are baseboard hot water. Zone 4 is domestic hot water with a circulator to a coil in Vaughn Top Performer insulated storage tank. System is 12 years old. Worked fine until recently. Seems the super store tank water is dropping below the point where it would normally call for hot water to its coil from the boiler. Odd thing is when zones 1-3 thermostats call for heat in the morning it is then that the zone 4 circulator turns on. It heats the tank water to what I assume is the high set point. Once it is at temp THEN zones 1-3 circulators turn on...despite the fact that they'd been calling for heat all along while the tank was domestic hw tank was heating up. The taco "zone 4 priority switch" is enabled and always has been. Question - why isn't zone 4 turning on when it needs its water heated? Why does another zone's call for heat seem to be needed to turn on circulator 4?

HVACNUT

Sounds like an internal problem in the zone board. Try swapping out the zone 3 and 4 cube relays in the board. Jump TT on zone 4 and see if the circ runs for the water heater. Next, remove the jumper from the WH and jump TT on zone 3. Does zone 3 run?
Again, it sounds internal. Also try switching priority off.

mtschneider1

Problem seems intermittent. Just turned all thermostats down, turned on sink hw and after a few mins...boiler and zone 4 turned on. Good suggestion above. Thanks! Will try that.

Patchogue Phil_2

So, what happened next?

newagedawn

the priority switch being enabled will always cut the heat loops out until the HW is satisfied, the zone panel should come with relays, maybe the one for HW is beginning to fail or the aquastat on the HW