Hmm!
One of the problems with a combi is the hot water flow rate. In a very simple way. Imagine you had a metre long piece of metal pipe and you put cold mains water in one end and heated the pipe with a blow lamp.
Now the water has only got a metre to travel before you want it to come out hot. So you need a lot of heat and the hotter or the bigger the pipe the more heat you need.
It's also why the amount of heat for the central heating side of a combi, is usually well within the amount of heat needed for the hot water. And why the bigger the boiler the more water you can get out of it.
So you may get something like a 12kW combi but the central heating would only require say 10kW. It is possible to get it wrong of course and get a boiler that is enough for the hot water but not enough for the central heating. So you have to get some idea of what you want first.
A condenser is more about efficiency than anything else. If you stick your hand in a boiler flue plume its hot I can tell you. But the heat goes to the atmosphere and is wasted. So a condenser recirculates it and makes it heat more of the water in the boiler. That's basically it. It isn't that simple though its just to give you some idea.
So basically a condensing boiler either of a standard type or a combi is supposedly more efficient than the none condensing boiler. And if you have got a lot of taps you need a big boiler and you need the water pressure and flow coming into the house to be able to supply all those taps as combi boilers usually have a lot of resistance and require decent pressure to push the water through it.
There are plenty of websites that will tell you more about combi's. But as has been said you are very reliant on them for both heat and hot water and they are reputed not to be all that reliable and so I would advise you to get yourself one of the repair plans going about.
