Hi I'm staying a friend's holiday house and there is no hot water.


The only instruction I have was to turn the hot water cylinder on at the wall.


http://s29.postimg.org/5enowyumv/photo_2.jpg


http://s29.postimg.org/ctd0pcgif/photo.jpg


On the right of the photo are two black taps.


The central one is labelled water but there is not audible sound when it is opened or closed.


However when I turn the far right black tap (See photo) I can hear either filling or draining. When I open it completely the pipe connecting to the relief valve starts to overflow.


What is the black tap to the far right controlling?


The taps on the left are faintly labelled "hot water drain" and "cylinder drain".


The taps on the left are tightened but I suspect the tank is not filling?


Thanks in advance!