This topic may have covered in the ebuild  but I haven't managed to track it down.

I am installing  a 500 litre unvented Thermal Store in my new build. Most of the main issues have been resolved, thanks to numerous contributions and discussions on ebuild and here,  except for control of the Thermal Store. 

The TS  will supplied from two sources - a 24kW condensing gas boiler, adjacent to the TS in a Plant Room,  and a 3 kW immersion heater, via a  PV diverting device. I have  3.99 KWp solar system installed

The TS will provide DHW via a 46kW Internal coil (mounted at the top of the TS) and low temperature water ( 25 C) UFH, via pipe connections mounted in the centre and bottom of the TS.

The immersion heater will be controlled by a temperature switch  and will be located at the bottom of theTS.

The boiler will provide heat to the TS via pipe connections at the top  and centre of the TS. 

My question concerns what is the best way to control the boiler and TS. My thoughts are to install  two temperature switches, one at the top and one at the  centre.  The boiler would be switched on by the centre ( stat ) at <50C  turned off by the top ( stat ) at >70C. There would also be  time switch//season  control, to ensure that the PV supplied immersion heater takes precedence over the boiler, especially in the main summer and shoulder months.

Any actual operating experience and feedback would be appreciated.

Sounds pretty much spot on to me. As opposed to a seasonal control, maybe a relay to hold the boiler off if the immersion is energised? That coupled with the time clock would be a good solution.