The 1st floor showers are Trevi-boost which relies on a venturi-effect mains water jet to add pressure to the mixed hot/cold shower. These do not work very well. The hot water cylinder (vented) has 3 hot water outlets: 2 for the 1st floor showers and the 3rd for the general hot water in the house. I plan to close off the vent so that the hot water cylinder can be pressurised by a pump placed in the water inlet feed to the cylinder. Any excess pressure caused by hot water expansion or other reasons will be relieved simply via the inlet pipe back up the cold water storage tank in the loft. Will this approach work?