On 16/02/2021 21:35, S Viemeister wrote:
On 16/02/2021 20:35, Chris B wrote:
Friend of mine has a leaking HW cylinder.Â* They have a very expensive
maintenance contract with BG so they have rung them up to come and
have a look at it.

"Oh you have got a very funny tank - its got 2 coils in it."

"Yes we know it has 2 coils, one is for the Gas the other is for the
back boiler behind the open fire in the lounge."

"It will take us ages to get hold of a cylinder of that size with 2
coils can you live without the back boiler?"

"Well yes its never been used since the gas was installed."

My question to the group, if you drain all the water out of a back
boiler system, does that preclude using the open fire?Â* IE will you
melt/damage/distort the fireplace/boiler?

I don't think it will bother them if the answer to the question is no
you cant use the fire - as it has not been used in 25 years - but they
would like to know if it MUST not be used rather than they choose not
to use it.

MUST not be used, unless made safe first.

http://www.heatingandventilating.net/womans-death-in-boiler-explosion-highlights-back-boiler-risk

The issue there was that the pipework had been capped and there was
presumably still some water left in the back boiler. Very bad idea.

As the other poster said, filling with sand AND LEAVING VENTED is
traditional, although TBH I am not quite sure what the sand filling
does. My woodburner is just a cast iron box; no firebricks so the back
panel sees direct heat. With a back boiler, it's the front face of the
boiler that sees direct heat. Its back face will get up to a similar
temperature by radiation, depending on how well it is cooled from
behind. You are not going to melt anything in a woodburner, although in
a coal stove (especially with smokeless fuel) the grate may get hot
enough to distort significantly.

If it were mine, and if I was unable to confirm with high confidence
that the pipework had not been capped (and perhaps bricked in) then I
would probably drill a few 3/8 inch holes in the boiler through the open
door. It should drill reasonably easily with a cordless drill and a
sharp HSS drill bit. Come to think of it, a couple of through-wall slits
with an angle grinder would have the same effect.

Also, back boilers are sometimes an optional "add-on" so it might be
possible to remove it, although you would probably have to do some
dismantling.