Following on from the earlier thread about "pumping under", I'm
seriously considering converting my friend's system to unvented - making
it much easier to get the air out, and hopefully solving the circulation
problems. [And hopefully not introducing too many leaks as the result of
the higher pressure!]

I am aware that I would need to disconnect and blank off the connections
to the F&E tank, and install an expansion vessel, pressure relief valve
and filling loop with pressure gauge. From what I can see, complete kits
can be obtained for 70 or 80 quid.

The question is where in the system to install these items.The boiler
and pumps are in an integral garage, surrounded by heavy workbenches,
tool chests and shelves - making them very difficult to get to without
moving lots of stuff. The F&E tank is in the attic above the airing
cupboard, and connects into the flow and return of the HW circuit.

The airing cupboard would be by far the easiest place to install the
kit. There is ready access to mains water for the filling loop. Because
the secondary HW system is unvented, there is a tundish into which
anything coming out of the hot cylinder's temperature and pressure
relief valve would spill - so that could also accept the output from the
primary circuit's PRV. There is an uninterrupted connection to the
boiler - albeit in 15mm pipe, and probably 3 metres vertical and 3
metres horizontal away.

The boiler's installation manual says to put the the PRV on the flow
pipe, close to the boiler and before the pump inlet. But that seems to
assume a single pump on the flow side, prior to any zone valves, etc.
But this system ain't like that! There are two pumps - one for CH and
one for HW - both on the return side, feeding *into* the boiler.

Are there any technical - or even legal - reasons for not installing all
the kit in the airing cupboard - some way from the boiler, but directly
connected to it? If so, could I put the PRV near to the boiler, and the
expansion vessel and filling loop somewhere else (preferably in the
airing cupboard)?
--
Cheers,
Roger
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