[hypoxia]

What Richard said. You can put a small circulation pump which is used in Mercedes Benz cars its 12v and made just for that function.
https://www.ebay.com/itm/157611551230?_s...BM9sb5lvhm

Then put a flat plate heat exchanger in that circuit run the hot water in and out to the hot water manifold. It works and as long as the aqua hot is hot you'll have hot water.
https://www.ebay.com/itm/267199422760?_s...BMkLSWl_hm

You always amaze me!