hi, sorry its took a while to reply, most people only answer questions in the main home and garden section and not the diy bit.
right, best boilers you can buy are vaillants or worcesters. you then need to decide what power output boiler you want which is determined by your hot water requirements and not your heating. the more powerful boiler you have the faster and hotter your water will be.
i was on a vaillant training course recently and there more popular model is the 31kw.
worcester do a 37kw model called the worcester bosch greenstar but it may be overkill for your needs.