Advice needed on sealing a vented system

[Jock Spanners]

Evening All,
I have an unusual customer who is bit of a recyling nut. Last year we installed a heat only boiler (only after it died) and changed all his downstairs rads. It's only a small 3 bedroom house but for some reason he resisted getting a combi. Now he's having a loft extension there's only going to be about 500mm of head between the F&E tank and the loft radiator. I am considering sealing the system by removing the F&E tank and installing an expansion vessel. It's not something I've done before but I've seen one working. Obviously his upstairs rads could be at risk and the coil so I was thinking of pressure testing it to 2 bar before. If anyone has any advice on dos and don't it would be appreciated.
Jock

 

[ShaunCorbs]

Low pressure seal eg 0.5 bar and blow off at 2 bar

 

[Jock Spanners]

Low pressure seal eg 0.5 bar and blow off at 2 bar

 

[Jock Spanners]

Low pressure seal? What's that and where would that go?

 

[ShaunCorbs]

Exactly the same as a normal sealed system but you just fill to 0.5 bar and set the pre charge in the expansion vessel to 0.6 bar and the blow off 2 bar