In article ,
"IMM" writes:
"Andy Hall" wrote in message
.. .
50kg mounted high up can create a substantial load.......

On a wall like a gable end? Which has racking strength from the roof
timbers too? Please.

Gable end is often not tied to the roof trusses at all.
In any case, it's not a very solid structure, so tying
it to the roof trusses does not necessarily gain a lot.
Also, it doesn't have any weight on it (the roof doesn't
rest on it) -- the weight is just that of the wall itself.
You shouldn't think of the mortar providing any lateral
strength (one hairline crack, as it will surely have, and
there's no strength in that direction). So just imagine
it's built of loose bricks with no mortar and decide
if you think it can support sufficient sideways weight.
Providing boiler's low enough that there's still many
times the weight of the boiler above the mounting point
and the centre of gravity remains inside the wall, you
would probably be OK. If there isn't much weight above
the boiler mounting points and centre of gravity when
taking the boiler weight into account is not still within
the wall, it's an unstable structure which could collapse
eventually. In addition to the displacement of the centre
of gravity, there's a question of if the wall is strong
enough to carry the weight without the weight pulling
out some bricks, which will depend on the condition of
the mortar (which in this case provides the frictional
force preventing this) and the weight of wall above the
mounting. Again, failure is likely if the weight above
the mounting points is not substantial, i.e if you
position the boiler near the top of the wall, or if
the mortar is not in good condition.

You can easily model all this with a child's building
blocks.

One way round this would be to get the neighbour on the
other side of the party wall to have an identical boiler
fitted on their side, with single bolts going
through the wall fixing up bother boilers. Then the
center of gravity will remain in the middle of the wall
so the structure is stable, and there's no force pulling
bricks out of the wall.

--
Andrew Gabriel