external leak?

[Marco1976]

Hello,

Since yesterday I can hear a hissing / crackling noise through my water pipes. I can hear this in the kitchen and in the bathroom upstairs. It is slightly louder upstairs.
So far no sign of damp.

Could it be an external leak?

When I turn of the stop tap in the kitchen, the noise stops. Note that after the stop tap there is a pressure relief valve if this makes any difference.

Thanks.

 

[Boilerman2]

To state the obvious if the hising noise stops when you turn off the kitchen Stop-cock then the leak MUST be downstream of this point! is it a pressure relief valve or a pressure reducing valve next to the S/C??