System for extension

Hi all,

I am looking to build an extension/ annexe so that my mother can move in with us.
Can someone give me some advice as to the best option for central heating and hot water?

We currently have a 3 bed (well 2 and a half bed) semi with 8 rads.
One bathroom
One downstairs toilet
Kitchen
We have a combi fitted at the moment a Worcester 24CDI which i find a bit underpowered ie water pressure drop.

With the extension i would be looking to add
kitchen
Bathroom
1 bed
living room

I expect to add 5 more rads.

Although this is to be almost separate to our house (there will still be a connecting door) i would like the option of being able to sell in the future as a 4 bed house.
So i was thinking it wouldn't be wise to have two separate boilers??

I am not worried about changing our existing system as we are currently renovating our downstairs and all the pipework is in the upstairs floor which i can access from downstairs.

Thanks

Aaron

Add an unvented cylinder for your hot water needs, have the combi just feeding the kitchen taps, the extra rads will not be a problem for the boiler you have.

thanks Gasman

Is there a minimum water pressure these need?
Its just that for some reason when we had the combi fitted there was a definate reduction in our mains water pressure

Cheers

Aaron

Twenty litres per minute flow for the unvented, the combi should not reduce the mains pressure, may need to have a new mains supply or at leasted checked by water board.

Thanks for your help Gasman much appreciated.

I will get mains supply checked

Thanks

Aaron

Would concur with GM, but with the addition of zoning the heating system.

You will also need at least 3-3.5bar cold mains pressure as the pressure reducing valves are set at around 3 bar to balance the system.

Thanks everyone for your help