On 18/08/2015 12:24, John Rumm wrote:

Not sure what your definition of expensive moving parts are, but one
might argue that a shower pump required to get a decent shower out of a
conventional cylinder would count as one.


The shower is downstairs. Upstairs we only have a (brand new!) bath and
basin. The current shower works fine - in fact, it has a pump and we've
turned it off as unnecessary.

Unless your mains incomer is brand new (no scale) there is no
guarantees you with get more than a trickle of water to filla bath.

As everyone else has mentioned, a decent flow rate and pressure on the
mains are prerequisites

People will tell yoi how marvellous mainpressure hot water systems are
but there are lots more parts to go wrong.

The two statements are unconnected... The second is possibly doubtful.

A conventional system has one valve / moving part in the cold cistern,
and probably a zone valve in the primary of the CH feed. So two in total.

An unvented system has a combined control valve on the inlet (over
pressure, and PRV typically), and a over temp and relief valve on the
side. Plus the expansion vessel. So in all five moving parts in place of
two - hardly "lots"

There is also no cold cistern to overflow, freeze, acquire dead
wildlife, or leak through your ceiling. No need for shower pumps.

There is no need to remove everything.
All you need is a new header tank (if it's a galvanised tank) If
plastic it will be OK.
And possibly a new cylinder.

Erm, that pretty much counts as removing everything.

The loft tanks are plastic. A bit sludgy, but plastic. They're also
under thatch which should help protect from frost.

snip

The old cylinder is poorly insulated. Yes this could be improved with a
jacket etc, but it will be difficult to get it to the standard of a
modern cylinder.

Secondly, the old cylinder will have a very low efficiency heat
exchanger. This will result is very slow recovery, and high flow return
temperatures for the boiler - leading to further loss of efficiency
there as well. A modern unvented cylinder will be able to take the
boiler's full output during recovery.

OK, thanks everyone. I've raised my concern over the downstairs bathroom
radiator - it has a large blister which might be full of water. But WTH
that's on a solid quarry tiled floor.

Andy