How big is the house ? 1,2,3 bed ??

How many people in the house ??

What system do you have in there atm ??

The heating side of things are fine they will run 10 rads easy and microbore isn't an issue,
but it needs a cleanser/inhibitor added to the system when being commissioned

Combis are really the cheapest systems you can get,

They have advantages and disadvantages.

Advantages;

Cheepest initial installation cost.

No wasted hot water (you heat what you use)

compact (no hot water cylinder, roof tank(s) needed)

Fairly good hot water pressure (depending on your mains pressure)

Disadvantages

Main one, Only one hot tap open at a time (otherwise pressure very poor)

If it breaks down, no back up

(conventional systems may have an immersion heater fitted to

the hot water cylinder as a back up)

If theres more than a couple of people living in your house I would say

don't have a combi, go mains unvented (the best system you can get)

same as anything, you pay for what you get