vortex2 wrote:
However are there any ideas for patching, especially ones that don't
involve draining the (I think, heating 'header'?) tank? Someone I know has
just suggested putting a plastic bag inside to stop the water getting out
(held in place by water pressure, in theory) and then patchingn the corner
with fibreglass sheeting as used for cars - which admittedly I've never
used.
[...]

Well I have a cracked/ leaky loo cistern which I "repaired" years ago with a
line of Silicone held in place by Duct tape. I never have replaced the
cistern and it's still waterproof. You might try that and see if it works
temporarily BUT the solution is to replace the tank or better still get rid
of it by upgrading to a sealed system.

Hmm, well I was just going to patch in short term, to give me some time
to figure out long-term changes/fixes. I think changing my CH isn't
quite what I had in mind today That, and I'm not sure another mega
discussion on CH systems is a good idea

.........and of course kill the rodents.

Going to dig in local Grocer type shop tomorrow morning, need to get
this sorted ASAP! Already have one trap, which I've put up there with
some lovely chocolate...

If you could hear the dripping i'm surprised you could not hear the rodents.
We had a similar problem years ago which was only properly solved by getting
a cat.

Well I haven't heard any up there, but this is above a bedroom... so
once I'm asleep then I don't tend to notice such things

My gf has cats though, but she's not moving in just yet...

--
Neil