Recently, our Central Heating has been waking us up in the morning when it
comes on. It makes a "wailing banshee" kind of sound. Before I call the
elders of the chuch to exorcise the house, I though I'd see what you all
might recommend.

I checked the header tank about a month ago had found it to be empty, the
ball valve stuck closed. That's fixed now, but clearly there was more water
needed in the system - I have been bleeding our bathroom radiator regularly
over the last few months.

We had a British Gas engineer round the other day who replaced the main CH
pump. He said that was (most likely to be) the problem, having worn itself
out when there was no water available to pump, but we still get the banshees
coming back. The boiler itself sounds a bit like a kettle when it starts
(high-pitched hissing) - it never used to. Typically, when I tried to show
the engineer, there were no noises. I don't mind the usual
expansion/contraction tapping sounds, but I don't like being woken up with
the CH coming on!!!

I'm not entirely sure where the noise is coming from - it usually only lasts
about 2 minutes, and I haven't crawled out of bed to listen to each and
every part. I am pretty sure that the noise is being sent round the system
and that it's not the radiator in my bedroom that is at fault.

Any ideas?!
Thanks,
Aelx