2 strange pipes beneath gutter (continually flowing water)

[S1D3BURN]

Hi, this is certainly a newbie question, but we live on a terrace and beneath our gutter, jutting out of the wall, are two plastic PVC pipes. Everyone on the terrace has them.

I guessed it was some kind of drainage from the roof, but the concern is that one of the pipes almost continually flows water (but does seem to occasionally stop).

If anyone has any ideas what these two pipes do I'd really appreciate it!...

 

[HERTS P&D]

Check the float valves in your cold water storage tank and expansion tank first.

Andy

 

[S1D3BURN]

Ah yeah - just turned on all the taps and low and behold it stopped - looks like I'm buying a ladder to get into the loft (we're new to the house)