On Saturday, September 5, 2020 at 5:34:27 PM UTC+1, Andy Burns wrote:
David Aldrich wrote:

The pump is located at the base of the hot water cylinder.
I am wondering whether we could move the pump to the loft
Would there still be any head between the bottom of cold tank and the
pump? If not you'd need to swap to a negative head pump.

Otherwise it's do-able, you need an anti-gravity loop on the output of
your flange to stop air getting sucked into pump, a non-return valve on
the output of the hot side of the pump, and air vents on both hot and
cold plumbing above the shower

see e.g. fig 4

http://www.free-instruction-manuals.com/pdf/pa_1001753.pdf

Thanks for your help. Given what you have written, and the fact that there wouldn't be any head between the cold tank and the pump, I think it's probably best to leave it where it is. Perhaps I should buy a quieter pump.