A storage boiler sometimes called a combined primary storage unit (CPSU) has the central heating boiler and hot water cylinder combined in one big box, this provides large amounts of hot water whenever required by the homeowner. It is similar to a combination boiler in that all the heating components are inside the boiler casing and there is no requirement for cold water storage tanks in the loft. However they do address the disadvantages of a combination boiler in that they can cope with much higher demands, being able to run a bath & and a shower at the same time.

The Ideal Istor He 325 will store 120 litres of water at 70°C this is then blended with the cold water to produce water at a maximum 60°C. The recovery time of the hot water is very short, between 7 and 10 minutes. Other boilers to consider are the Potterton Promax HE Store this has various capacities up to 150 litres, or the 170 litre Glow worm Ultrapower sxi.