I have been trying to trace a fault at an old ladys house for a while , without success until now. the rcd would trip when she plugged certain appliances in to either of the two ring circuits in the house , but the IR readings where ok when tested .There was no sleeving on any of the cpcs at the sockets, so i rectified this. this cured the problem for 8 days. Next checked cables in attic for rodent damage all ok.After this i unplugged all appliances and then plugged them in one at a time untill i narrowed it down to an electric fire in the living room that was fitted in the fire place. When i pulled the fire out a brass **** came off in my hand from the front . This turned out to be a door **** with a screw thread coming out the back for fixing i n a door etc.this had been touching the element through the front of the fire. When i told her she said Oh ,i just thought it looked nice . Turnes out she never actually usews the fire . Arhhh. :_|