We have a Vaillant ecoTEC plus 837 with no concerns.
http://www.vaillant.co.uk/installers...2/combination/
We chose this one over the smaller models (which still had suitable central heating capability) because we wanted high hot water flow rate for decent shower.
If you call Vaillant they can assist in calculating the size boiler your property needs. Bosch also have a reputation of being reliable and helpful.