Removal of 2 combination boiler and the fitting of an unvented cylinder

the picture on the left is of 2 combination boilers in one house. one feeding the upstairs and the other the down

unfortunately it is a large house with 3 bathrooms and other wash rooms in and 3 showers

But the occupants complained that it took too long for hot water to reach the  taps at the far end of the house and also took too long to fill the baths 

plus the fact they want a lager capacity bath 

in the house was a standard domestic gas meter which could not provide enough gas to feed both simultaneously  

So I was asked for a better solution

so I suggested

 only one boiler 28KW (100,00BTU)

 an unvented cylinder with secondary circulation 

3 zone valves (S Plan system) one for the hot water controlled by a timer in the kitchen and the built in cylinder thermostat. the other 2 zones vales are each controlled by a programmable room thermostat (Danfos TP5) one is for the downstairs and the other the upstairs.  

the secondary circulation was achieved by connecting the existing upstairs hot water pipe to the top the the cylinder, connecting the downstairs hot water pipe to the secondary return concoction, then connecting both system together at the far end of the house 

a Bronze pump (controlled by the timer) is used on the return pipe so the hot water can flow around the house so hot water is instant at all the taps at the times required