On 17/08/2015 23:33, Lobster wrote:
On 17 Aug 2015, Fredxxx grunted:

On 17/08/2015 22:07, wrote:
On Monday, 17 August 2015 21:36:39 UTC+1, Vir Campestris wrote:
We're having the whole lot stripped out - want one that isn't 30
years old and badly insulated for the new boiler - and the installer
has suggested a mains pressure cylinder. Apart from anything else
the warranty is longer!
What do the team think?

Depends on your mains pressure and flow.

On the upside
- no loft tanks
- mains pressure hot water for showers

On the downside
- higher initial cost
- requires annual safety check

- requires tundisk and pressure relief pipework
- may also require pressure regulating valve and pressure relief
valve on the cold mains inlet as well

The above two items are really just part of the installation though; ie
the higher initial cost. But I suppose could cause issues depending on
the location of the installation.

Indeed.

On the downside I'd add that you might want to consider that if you are
using an existing old CH system, to bear in mind that hitherto it's been
used just at low pressure; will it stand being used at mains pressure,
or might there be a partially corroded weak spot in an old radiator
which will blow in spectacular fashion.

I think you are conflating some issues here... the "mains pressure" bit
here is the DHW in the tank and has nothing to do with the primary
heating circuit that the rads are or. That could be a traditional vented
arrangement if you wanted or a modern "sealed system".

The situation you describe may be valid if converting a whole CH system
from vented to sealed.

But then again, on the upside, if ever a pressurised system does leak
for whatever reason, there's only a finite volume of water which can be
ejected, compared with an unvented system which would leak forever if
allowed.

If the DHW leaks, remember its connected to the mains ;-)

--
Cheers,

John.

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