I had to bleed my radiators the other day and all went fine, turned off central heating and hot water as usual. Unfortunately about half way through the process my elderly dad turned the upstairs hot water tap on fully having visited the loo and basically we now have no water coming from any hot tap including the shower. Do I have an air lock? I have a modern gloworm slim combi boiler, pressure is at 2.3bars and the cold water and central heating are both working fine.