Hello, here is the picture of a heating riser digram consisting of a Teledyne Pennant 400mbh-input heating boiler, inderect Turbomax hot water heater, and a single zone for radient heating.
Application is for a spa/massage/therapy (cellar floor).

What would be the controlling wiring layout in system like this? What would a radient heat thermostat be connected to? How is all this interacted with temp. sensors on radient heat manifold, what gets the priority and what does what step by step...
And how is the hot water heater made to have a priority in this?

Call an engineer. We try to help with furnace failures but designing a wiring sysyem is asking a bit too much.