Calorifier and expansion tanks.. ?

[saltwater_gypsy]

I think the mystery valve is a temperature control for 40C to 60C. I have the same tank on my boat and a B&Q check valve stopped the hot-cold mixing problem.

 

[Danny]

[ QUOTE ]
Am I right in presuming any type of accumulator would work...............Oh, Danny, what type of one way valve did you fit ?

[/ QUOTE ] I got all these bits from ASAP. I found them an excellent company to deal with. If you get an adjustable accumulator you can "tweak" the pressure if necessary. The NRV was the standard one from their range.

Incidentally the NRV is necessary because of the second accumulator. If you don't install it the HW stored in the accumulator can flow back when you open a CW tap.