New combi boiler - unvented system

15 Aug 2013
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United Kingdom
Hi all,

New to the forum and hoping for some impartial advice on our new boiler/unvented high pressure system.

We are in the process of extending our house, which will be a relatively large 4 bed with 1 bathroom and an ensuite shower room. We are having a new boiler installed, coupled with a Megaflow unvented high pressure cylinder. The plumber has suggested a Worcester-Bosch 29CDi Classic Combi, which I found quite surprising as I thought system boilers were normally used with an unvented cylinder. His rationale is that a combi is suitable because it can be isolated into 3 different zones (the cylinder, the heating and the underfloor heating). Given that the boiler is to be mounted downstairs in our new utility room (at one extreme side of the house), he said it makes sense to have a combi which will supply hot water on demand to the sink in that same room, with the Megaflow doing all the heavy lifting upstairs with the bathroom, ensuite, etc.

Being of limited knowledge on these matters, I’d be grateful for any views on whether or not this sounds like the right thing to do.

Thanks in advance.
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It is a little ott for a house as yours is described.

But the idea is not without merit. We've done it in bigger places where the kitchen or utility was remote from the rest of the hot water points of use/airing cupboard.
Thanks for the reply. Just to clarify, the house will be c.2,500sq ft in size, so a fair bit of distance between the boiler and sinks, showers, cylinder, etc.
yes it sounds as though your installer is giving you decent advice, the cost of purchasing a combi v system boiler isnt great and sometimes the combi is actually cheaper to purchase as they make a lot more of them
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Glow worm ultra power.

Combi and unvented cylinder all in one with a immersion heater back.
Will work as just as a combi if not many in the house.
Never run out of hot water. Will outperform a 300litre unvented cylinder.
Do you fit anything?

edited that slightly for you dan :p

op, why not secondary circulation if its a big place and your doing alot of work. More to go wrong on a combi. They are often cheaper cos manf get their money back in spares :p

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