In article , Doctor Drivel wrote:

????? Fit 300 litre and is less than 15 litre?

No, 15 litres is 15 litres or less.


But tell me more about the servicing requirements. When Nu-Heat replaced
my failed vented heat bank with an unvented one because they didn't do
vented ones any more, no servicing requirement was mentioned.

Nu-Heat
Look at the presurised thermal store (heat bank really):
[...]
Nu-Heat use a plate heat exchanger, not an ingeral coil, so no G3.

That's not true of all Nu-Heat supplied stores. Mine has a coil.
(In fact two, one DHW, one underfloor heating.)