Andy Hall wrote:
The cylinder is probably 15 years old and is lagged with expanded
polystyrene, I guess. It is an indirect cylinder with an immersion
heater. Looking at the catalogues it appears an identical cylinder is
available with the correct configuration of inlets and outlets. So
far straight forward to replace ;-).


Well yes, but will always take longer than you think. Nowadays, they
are better insulated so do check external dimensions if the cylinder
is a tight fit in the airing cupboard.

Agreed - my "it'll only take a few hours" cylinder swap a few months ago
tunrned into a whole weekend - including the usual mad dash to B&Q on
Sunday afternoon before it shuts for extra parts!

One other thing - are you absolutely sure that all the inlets and
outlets are in identical places? We though they were, but when we got
home it seemed that the top inlet for the coil was higher than on the
old one - presumably because the coil was larger to comply with Part-L
regs.

With respect to replacement. There is a shut off cock for the cold
water in and a gate valve on the CH boiler hot inlet to the coil
(think it is the inlet). There is no isolation on the other side of
the coil (outlet).

My question is do I need to drain down the CH system to replace? What
crossed my mind is I could put a cork into the outlet from the CH
header tank in the loft that should stop drainage from the outlet side
of the coil when I disconnected, at least in theory. Any thoughts on
this?


There is a technique where you can put bungs in the vent pipe and the
feed pipe from the roof tank. Normally this is for radiators swaps
etc. I am sceptical that you would get away with it for this because
the pipe is 22mm normally and you are likely to get water running out
more easily. You might be able to remove the pipe quickly at the
cylinder and bung that end as well, but I'd suggest draining down and
not having the hassle

I agree - remember, you probably won't have to drain the whole system,
just to the point below the cylinder.

With respect to the immersion heater. Do you think I will be able to
get it out of the old cylinder bearing in mind it has been there 15
years or so? I know I will need to buy/rent a spanner but are these
things in to stay once they are this old? Further, do you think it
sensible to replace the immersion heater anyway as I guess they don't
last forever?


If it's the original, then I would dump it along with the cylinder.
New ones are also safer since they have an extra safety cutout to
reduce the risk of boiling if the thermostat fails.

Definately scrap it - I can't imagine it would be easy to get it out of
the old cylinder anyway. We got a new one for less than £15 so hardly
broke the bank!