Advise on new boiler/CH/HW set-up

[JimLoskot]

We are having a whole new boiler/system/pipework and am after some advise with regards to the type of setup we need.
We have a largish 4 bed victorian semi which is going to have 2 bedrooms with en-suite, a family bathroom, a downstairs toilet. Going to have 14 radiators, 2 possibly 3 showers(will not be electric), 1 bath, 4 toilets and 5 sinks.
I have replaced the water pipe to the main with 25mm MDPE which connects to the water meter so the pressure/flow rate into the house should be good
From the research I've done, it seems we need a regular or a system boiler.
Our plumber is a viessmann-installer so we will get the 5 year warranty.
We are looking at either the viessmann vitodens 200-W 35kw or the worcester greenstar 40cdi. I am not overly sure as to the benefit of either except the extended warranty. Any others worth considering?
The main issue is the that we have a attic conversion which has an en-suite with shower which will be above any gravity-feed tanks that are in the other part of the loft.
As we want the showers to have good pressure/flow and not be electric, our plumber has suggested either a negative-head pump or a pressurized cylinder. I'm not really sure what to go for as I'm starting to get well beyond my limited knowledge.

Any advise on what set up to go for would be gratefully received.
Thanks
Jim

 

[patsmotors]

1-get a boiler that engineers will be happy to repair in the future.
2-unvented cylinder will be best if existing water flow rates are good.
3-be prepared to spend a few ££££.s

 

[Andygasman2010]

As said, unvented is the way to go so long as the incoming mains is good enough.

Worcester 30CDi System with integral diverter, FW100 weather compensator, then however many zones you want wired back to the boiler.

Depending on your final set-up if you go with a system boiler you may need to split the boiler and system with a header. It sounds like it'll be fairly large.

I don't know much about the Viessmann gear but i hear it's good. Worcester also offer a 5 year warranty.

 

[ALEC1]

both boilers are good providing that you use the weather compensation which basically varies the flow temperature in relation to the outside temperature, the cooler the weather the warmer the radiators.

But there is no point in oversizing the boiler 14 rads is probably a 20kw heat load and the unvented is unlikely to have a could big enough to take more than 24kws..

it costs a bit more a bigger boiler and gives people peace of mind but its all a waste of money as the radiators won't emit more heat than they are designed for!

 

[JimLoskot]

Thanks for all the replies.

So the 40kw worcester or the 35wk veissmann will be too big then. would the 30kw boiler in either be better? its a fairly big house(4 bed, 2 ensuite's, 1 bathroom, 1 large reception rooms and a large kitchen diner with a small downstairs toilet and util room and 2 cellar rooms where I plan to put 1 rad to put a bit of heat in every now and again to ward of damp.)

Is unvented the same thing as having a pressurised cylinder?
will this give me a good shower and be able to run other taps in the house at the same time without affecting the shower?

What water pressure and flow rate do I need to run an unvented system?

Thanks again in advance
Jim