John Rumm wrote:
Tim Downie wrote:

If you buy a good quality cylinder (I'm going to get an Oso) and
have the appropriate safety ancillaries installed I can't see the
point in wasting time and money on an annual inspection by someone
who has gone on a 0.5 day "course".

It's still a pressure vessel with explosive potential (more so than
a vented cylinder). Safety ancillaries can and do fail. May not be
hard to check yourself if you know what you're doing but I'm not
sure I'd want to live on the other side of a party wall to one that
hadn't been inspected for years. For most non-DIYers, annual
inspection probably makes sense.

I think there is another misconception here as well. The only time a
pressurised water cylinder is at explosion risk is going to be when it
has the possibility of being heated to over the boiling point of the
water content. Then there is the risk of the explosive production of
steam should it rupture.
For a cylinder heated via a water flow from a boiler, the chances of
super heating it seem minimal.

You're forgeting Sods law. The only time the safety valve is likely to get
stressed is when your CH boiler packs up on Christmas Eve and you turn on
the immersion element that's not been used in years. A sticky stat in that
and a sticking safety valve can then lead to an explosive situation. A
vented cylinder needs another level of system failure before it can blow.

The risk is low but it's a hgher risk than an vented cylinder.

Tim