Vehicle passed mot but on return from Porth started to develop a water leak. On return to depot we put back on pit and investigated where leak was coming from. It was found an electrical loom had chafed through a heater feed pipe. We removed pipe and put a new piece of hose over hole repositioned loom and refilled system. We then found the coolant level light would not go out so more investigation we found the probe in the header tank feed cable had a broken wire so we made good a repair and the light now works properly. As engineers we like to see warning lights and gauges working properly on our buses as it can stop potential disasters we can ill afford.