bosch worcester 20/25 hot water stop cock?

hi all. got a leaky tap in an old house, nothing unusual there, unfortunatly a couple of problems arose on the way. There are no inline isolation taps to the taps on the sinks (soon to be resolved), and as the house is old and cornish, the mains water runs through the middle of it, for the whole street and doesnt have a stop cock! So the next step is to isolate the boiler. Joy. The previous owners who had the boiler installed managed to lose all the instructions ect so i cant find the hot water isolation tap. Any help would be very gratefull, and you may possibly save the sanity of all who live here, when the constant dripping sound can finally stop!!!!!!
Cheers
Chris