Yesterday, the stepson grumbled about a noise in the attic. I got the ladder out, and the lamp-on-a-clamp, and set out along the z-axis to have a nose around. There are two tanks in the attic, a large cold one and a smaller warmer one. The small one was howling, singing, going large with the drum-and-bass. I took the cover off, and waggled the float up and down a bit, and the noise stopped.
For the past year or so, the water out of the hot taps has been nicely hot. Today it is hot. Great clouds of steam arising from the kitchen sink, just like the old days when IDS was in charge.
I have no idea if these two events are related. My knowledge of plumbing extends just far enough to know that the tap with the blue on it is the cold one and the tap with the red on it is the hot one. But it's good to have hot water that's actually hot, even if it surprised me when it started.