Overflow pipe is leaking

[mackandmutley]

Wondered if somebody could give me a heads up. I am in bed and have now worked out that the tapping noise I heard last night and can now hear again is not the dog tapping but the overflow pipe leaking onto the patio outside the window. The heating has just gone off, i.e. has been leaking while heating on. Wasn't leaking earlier in the day or indeed prior to 1 hour ago. Any ideas where I need to start looking in the morning. Some Facts:-

New Gloworm boiler fitted 2 years ago
Cold tank in loft and little central heating tank next to it, both have overflow pipes exitng next to each other, don't know which is leaking.
no mucking about done on system for well over a year, all has been ok
house is 1970's 4 bed detached

Any pointers where to start?

Thanks

 

[twgas]

First things first, find which tank is overflowing.

 

[Armo74]

Turn your hot water tap on, if the overflow stops dripping then it will be your CWSC the larger tank of the 2. It may just be a faulty float valve.