Boiler for unvented system

[mazdaq]

Hi
I'm thinking of changing my boiler to a Greenstar 40cdi boiler. I have an unvented indirect hot water cylinder. No cold water tank.
Is this boiler suitable for my system?
I thought it was but I looked at the product info document on this page and the diagram shows a vented cylinder with central heating and hot water feed tanks in the loft, neither of which I have.
https://www.worcester-bosch.co.uk/products/boilers/directory/greenstar-cdi-classic-regular
https://www.worcester-bosch.co.uk/f...7/updated_links/gas/CDi_Classic_-_Regular.pdf
Maybe an expert here could confirm either way for me please?
Thanks
Chris

 

[DP]

Why do you need a 40kw boiler.

 

[mazdaq]

Currently extending my house - will be 5 bed, 4 bath house when done. Currently have an 18kw boiler. Also installing underfloor heating, so I think it is going to struggle.

 

[mazdaq]

I guess what I really need to know is what is the difference between a regular and system boiler, and which one is appropriate for my setup? I think the answer is a system boiler but would quite like that confirmed.

 

[fezster]

A system boiler or a heat only boiler will be fine for your setup, if you have a sealed system. The difference is that the system boiler will have the pump and expansion vessel inside it, whereas with a heat only boiler, your installer will need to add those separately. Personally, I prefer separate, as it means they can be changed out more easily, with different options available. Whereas a system boiler will need manufacturer specific parts. However, if space is an issue, a system boiler may be more appropriate.

If you have an open vent system, then you will need a heat only boiler. Another option would be to convert to a sealed system.