The solution is to disconnect the instantaneous feature of the boiler and use it as a standard boiler. Solar heated water will be stored in a new twin coil solar cylindert. This is not particular complex, but requires some re plumbing and wiring to be done.

A three port mid position valve is required, along with new Y plan controls to provide independent  hot water and central heating controls. Cold mains will need to be run to a fill and expansion tank (also known as F&E or Fortic) on top of the new solar cylinder, or a new cold water tank in the loft, with a cold water feed to the cylinder. A cold water tank in the loft will generally provide a higher head and better pressure.

We recommend that 22 mm diameter pipe is used on the hot tap circuits to ensure a good supply of hot water to the taps.

It is advisable to leave one outlet on the domestic boiler outlet from the boiler usually a tap in a utility room but should be one that is used rarely. Alternatively use a service tap on the DHW outlet of the boiler which is required by some boilers that have safety features that expect a certain temperature and pressure. In addition, it will avoid potential invalidation of the combi's guarantee.