On Jan 31, 8:36*pm, Kostas Kavoussanakis
wrote:
On 30/01/2011 20:09, Roger Mills wrote:

On 30/01/2011 19:47, Kostas Kavoussanakis wrote:

I too am considering the options in case my 25-yo boiler gives up the
ghost. The combi needs good pressure mains, I believe; have you got it?

It looks like, if you are upgrading or replacing (as opposed to
installing fresh), the combi is the most drastic option.

Indeed. Replacing a stored hot water system with a combi often involves
a lot more plumbing changes than installing a replacement conventional
boiler.

Thanks Roger.

I see from the
wiki and from the Vaillant and Worcester websites that there are two
non-combi options: open-vent (the same as what you and I have) and
sealed system (which only does away with the cold-water tank). I am
still not clear of the benfits of each set-up, so I will stop here.

If you are referring to a non-vented stored hot water system, this has a
mains pressure cold feed to the hot cylinder rather than having a
gravity feed from a cold storage tank. The advantage is that you get
mains pressure hot water, and you don't have to accommodate a cold tank..

Ah, I thought that modern open-vent systems might pressurise the hot water.