Adding indirect to 2 Zone Greenstar w/ circs & SR502 DHW priority issue

Ant1

Hi, I'm adding an indirect DHW tank to a Greenstar boiler I installed a few years back.

My dilemma is this: if I wire the DHW pump to the boiler, the heating circulators will still spin because they are controlled by the SR502. Had I originally used zone valves and a single system circ this would not be an issue since the system circ can be controlled by the boiler.

I was thinking today that I could remove the jumper between ZR/ZC in the relay panel and power ZC from the connection for a system circulator in the boiler, which is currently unused but would switch off on a call DHW since the boiler has a built-in DHW priority.

I sort of tried this out today and it didn't go as planned. I shut off the service switch and I removed the ZR/ZC jumper, turned power back on, and forced a call for heat, the circulator did not come on, which is what I had expected. I then jumpered ZR and ZC in the panel and the circulator ran as I expected. however when i removed this jumper the relay held and with no power to ZC the circulator continued to run. I then removed and added the call for heat and the SR502 operated as though the ZR/ZC jumper were still in place.

My understanding of the ZR/ZC circuit was that if the SR502 is used with a triple aquastat the power originates at ZR and the aquasat will open that circuit if the temp is below the low limit to prevent the circs from running until the boiler heats up

So my question is: Is there a problem with that relay in the SR502 or is there something else happening in the ZR/ZC circuit in a triple aquastat that i'm missing?

I will probably just rezone with zone valves which will solve all my problems, just thought I had found a creative solution and am now curious. Any insight would be greatly appreciated