Can you have mains pressure cylinder on a back bolier?

[rodhague]

I have been told that I can't have a mains pressure unvented hot water cylinder with a back boiler on a wood burning stove as the heat source is uncontrollable.
Is there a method to make the heat source controllable?
I was imagining that if the cylinder was at its maximum temperature then if there was a divertable route for the water to go so it bypassed the cylinder and went to a heat dump in the loft before returning under gravity to the back boiler that this would mean it was controlled?

 

[SimonG]

H2 unvented cylinder

Heating innovations h2 panel.