Stubborn white webbed mould

petersts

I’ll try the bag over the copper pipe and monitor it. It’s definitely from our boiler I’ll check the other pipes for leaks too. 

Could the outside tap have a leak somewhere inside the brickwork? 

It’s in a similar area to where the inside white webbed mould appears. If it is I’m not sure how we would access it to check. 

Lorian

Stand outside and watch it when it's pouring down. I'll guess the gulley at the top of the rainwater downpipe is blocked causing the gutter to overtop.  I wouldnt put anything over the copper blow off pipe. It's either wet inside to touch or it isn't.

But if that white pipe is you condensate pipe that's going to freeze as soon as it gets cold, you should check what that is actually draining in to as that could equally be causing the damp.