I'm in the process of having an extention built which includes a new bathroom and on suite. Both will have showers and i do not currently have a shower. This will make my house a 3 bedroom the boiler i have does the job but needs chamging.
My daughter has decided to renew her v. old gas boiler, with a Worcester Greenstar ( part of the well reputed Bosch group ), but she will be retaining the electric shower.
My own Gloworm gas boiler ( vented system with 210 litres of hot water storage ), has been replaced with a Potterton Promax 28 HE+, with the loss of stored hot water.
If I was doing the job again I would try to incorporate the Megaflo type of hot water storage, complete with its immersion element.
The BAXI / POTTERTON / MAIN group is at a cheaper end of the price range, but parts are cheap, readily available, and the boilers are familiar to maintenance men and are built to be easy to work on / in, without causing injury, from steel sheeting / poor access etc.
Some of the most reliable boilers are not backed-up well with a large network of well-trained tecnicians.
BOULTER is part of the BOSCH group, but is not well known in the UK but has a long history of excellent service on mainland Europe, so I would not consider that brand where I live, in the extreme north of Scotland, as I expect support will be very patchy.
Unfortunately, we suffer from a dearth of heating engineers, and a surplus of plumbers who are employed in firms where only the boss has the training to be registered, so he is never "HANDS-ON".