Complete novice needing a new system

[bice]

I have got the builders in to build me a side return extension in a four-bedroom terraced house in South London. It means remodelling the kitchen, putting in a shower room and ... sorting out the plumbing.
We have an open vent sealed system with an Ideal Classic LXFF boiler, about 8 years old, a hot water cyclinder in the airing cupboard, a cold water tank in a roof occupying narrow attic space we cannot use, and a red pressurised expansion vessel in the main attic.
The builders immediately suggested a combi boiler as a replacement, but I am very wary of this. I am no plumber but I have read up on hot water systems on sites such as this one and miketheplumber etc.
Our boiler works fine, but certainly is overdue for a service and is not a condensing boiler. So the building inspector may insist I change it if, as I want to do, I move the location.
It may be a good idea to replace it anyway as it scores only 76.2-77.2 on the sedbuk boiler efficiency site, or 'E'.
We also want a hot water cyclinder. we have a copper one, wrapped in an insulating duvet. it works fine, but may be inefficient and time to change it. Its location is changing.
I think the best course is to revive the feed and expansion tank in the attic, which is all in place, and scrap the sealed, pressurised system that we fitted about 8 years ago.
There are no space saving issues, as the cold water tank is not using usable space. And we want a hot water tank for an airing cupboard.
What do people reckon: I should ditch the pressurised system or stick with it? Should I keep the Ideal Classic boiler or replace with something like a Borsch Worcester 30 CDi, or a Vaillant Ecotec.
Any thoughts gratefully received.

 

[truemanufan]

Personaly speaking combi is more economic and energy efficient however if u do get a combi there no need for any tanks because there would be no need for them!

 

[moony]

you dont say how many bathrooms you have - if 2-3 then i would suggest an unvented - if the one mainbathroom with an en suite with elecy shower then a 30cdi will be fine - get rid of anything ideal (personal preference) worcestor are the name everyone goes after - but if your in the know matey give remeha a look - i fit remehas for anyone who isnt brainwashed by worcestor - really compact and quiet - 5 yr warranty.excellent after sales.

 

[tamz]

The Classic wasn't a bad boiler, reliable enough and easy to fix, but you may be forced by building control to change it as it is moving. Also moving it can create problems. Depends on your budget and what BC will let you away with. If you keep it why would you want to convert the system back to open again? Totally unnecessary.
You will benefit greatly from switching to a mains fed system, combi or unvented.
A combi is fine in the right situation and usually cheapest to run but they have their limitations as far as flow rates (that is why people complain, fitted to an unsuitable system). Don't expect to run 2 showers simultaneously from any combi. (a storage combi excepted). Your best bet would probably be an unvented cylinder and a system boiler.

As for which boiler?
Pay your money and take your chance. Ask 10 installers and you'll probably get 6 different answers for varying reasons. It is like buying a car where choice is concerned.
The best people to advise would be the guys actually seeing the job and you can do your own research to suit your needs too.