Now I am back in the UK I have had time to do some research
. The Red Varem pressure vessels/accumulators that are fitted by FP ARE suitable for potable water
. Apparently sometime around 2008 Varem changed the colour to blue or white to differentiate potable from heating
applications. Before then they were all red. Although the membranes and flanges are available as spares costwise its cheaper to buy a complete unit. I have just purchased a replacement unit - really not much option - variable pumps are a ridicious price
adding more unecessary complexity. This unit has a 3/4 BSP male thread so an adaptor to fit a 1/2 BSP female is required. Euroboiler spares sells the new white version accumulator at the lowest price
in the UK I could find £21.48 inc. EU Vat, non Eu price about $29. They will deliver around the world, here is the link and a photo
of the new unit.
EV 310 Varem 8 Litre White Potable Water Expansion Vessel