However, the water pump kept being triggered every now and again, leading us to think that there was probably a leak somewhere. On Friday evening, I was out and James had another look at the compression joints to make sure they were tight. In the process of tightening them, it seem that he damaged further another section of pipe which was already weak and leaking slightly. Plumbing emergency Number 2! Unfortunately, this section was inside the wall. The pipe exited the hot water boiler, made a right angle into the bulkhead, down between the bathroom wall and bedroom wall, and back out into the bathroom. Quite why, we can't work out, except perhaps for neatness.
We decided that the simplest way to fix this was to cut off the section which went inside the wall, and reroute the pipe straight down from the water heater to the T junction with the shower pipe. A trip to B&Q later, we had all the parts required to fix the problem, it didn't take long to put it all together. We do, however, still have a redundant section of pipe embedded in the wall, as we'd have to take the bedroom wall apart to remove it!