I got a thermal store tank from Navitron just before xmas. Luckily it came with 28mm connections direct to the tank as we found that the flow from the boiler up & through the 22mm unions and into the boiler coil wasn't sufficient- not blocked, just very difficult to push water through. Anyway glad the 28mms are there. We now use the boiler to gravity up HW to the tank water itself- works spot on to stop the boiler 'boiling' and having fitted a pump in that circuit we can later pump the hot water back down into the boiler and then off to the rads- great for a quick start on a cold morning, but you only get 1hr at good temperature and another at mediocre heat before the reservoir is all cold.
Mind you its only 260L and we have 11 rads in use with lots of long microbore runs too
It would work as Tangent twin wants. Wouldn't give you hot water for the taps though unless you have the high recovery extra coil fitted- we specced that on ours and although a bit pricy for a few turns of finned copper pipe and a mixer valve- it works well-
System doesn't use a neutraliser
Plus we have very soft water up here- I gather hard water areas will clog up the recovery coil piping in a few years
Looking forward to when I've saved up for the solar coils to add to it...not sure if it would be likely ,say with 30 tubes, to provide any radiator heat besides hot tap water though.