Very impressive.
I use to run a twin inlet and outlet on a stainless calorifier from radiator so it recycled through twice (same principal as yours). Use to recycle excess water through WFP tank when pole hose shut off like yourself so pump continuously circulating water until shut off on flow controller.
Used a longer length of brass hose after the pressure release valve as advised for safety reasons and used a metal 10litre diesel tank instead of a plastic tank as they are less likely to lose vapour gases or expand in the summer months if in direct sunlight, less chance of tank exploding.
Use to get temperatures above 100 degrees so use to turn it off by midday tops.
Well done