quick thought mate....most diverters have little sliding lever on the side ..(just under the head above the brass body )it sticks out about 1cm... if you have one you can slide this along and its got a little cut out in the side of the head that the lever can rest/stop in....this manually opens the valve and lets water through....you may get hot water and ch as the valve is fully open.......i sometimes use this a temporary measure to to get some heat back on ...