hi guys, can anybody give me any tips how to check, if my outlet valve on my storage heater is opening or not, the actual knob is broken and i've tried turning with a pair of long nosed pliers, i can turn the spindle but i do not hear any valves opening and closing, i guess if i take the front panel off it does not show the actual top of the heater where the valve is situated, is it easy to take the top cover off to see the shutter opening or closing, or does anybody have a drawing showing how to access it, thanks in advance