For some time (week) water could be heard flowing in the pipes when in the bathroom when nothing was in use. Over the last few weeks this has got worse.
Plumbling in house is quite simple. Iron pipe from cellar straight up to under bath (feeds bath, toilet, sink via copper), then across to back of house where it goes to copper to feed the combi, downstairs sink, and toilet.
No sound is heard downstairs, but can be heard in the boxing where the pipe passes to the rear bedroom towards the boiler and downstairs. There appears to be no flow after the pipe goes back downstairs.
Heating/all taps etc are off. As combi is fitted there are no tanks at all.
Can anyone suggest what is causing this noise? Is there is a sound there MUST be a flow? where could it be going.