For years I have had a problem with the electrics tripping at random, never been able to pin it down to a device or segment of the ring.
But now I have a halogen heater that is guaranteed to trip the RCD on the faulty ring, so I can use this to test segments of the ring and by a process of trail and error find the problem area.

My question is: The halogen heater trips the RCD when I plug it in to any of wall sockets except the two closest to the RCD. When I plug it into either of these two sockets it doesn't come on. There is power there but the heater does not heat.

What is going on?