On 17/03/2018 21:08, Cynic wrote:

There are as you suggest "safety features but unless correctly installed and commissioned the risk remains. Too many bodge artists out there!

Well the bodge artists are easy to dodge, install it yourself, then you
know its done right!

The safety features on the cylinders don't need commissioning as such -
beyond a quick twist of the test knobs to check they pass water to the
tundish.

There is a valve assembly on the inlet that usually combines a strainer,
pressure reduction valve, pressure relief valve, connection to the
expansion vessel, and outlets to the cold feed on the cylinder and a
balanced pressure cold feed available for use elsewhere. I suppose you
could install it backwards, but it would probably just result in a
system that does not work at all. The side mounted overtemp/pressure
valve is a special fitting that nothing else is supposed to fit. So it
would be difficult to omit it. I suppose you could connect it to a pipe
and blank it off, but that would still in the grand scheme of things be
less dangerous than say blanking off the vent on the vented cylinder.

The risk of a steam explosion does not exist with indirectly heated
unvented cylinders - you need either immersion heaters, or an
inappropriate connection to a solid fuel stove etc. (plus the defeat of
all the interlocks).

You can bodge dangerous hot water systems of all types (and the dangers
are not usually ones of explosion, but include leaking, flooding,
scalding, breeding legionella, back contamination of the mains supply,
and tanks falling through ceilings etc).


--
Cheers,

John.

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