The tampering with the heating started in the office. My radiator made a heck of a racket! And in the end I decided to bleed it. That shut the thing up. (And so far it can keep up with the heat lost! So far I'm chuffed with my office insulation.)
That weekend I also figured I should pay attention to the heating at home. It had worked initially, but some time ago it seemed to have switched itself off, for no apparent reason. And doing something about it had always ended up at the bottom of my to do list. The weather wasn't cold enough yet to make it a priority! But I figured I had to make sure I worked it out before the weather would turn cold, as it inevitably would.
I googled a bit what can go wrong with heating. It was only the heating; the shower worked fine! And it lead me to focus on the thermostat. I pried it open. Maybe the batteries were empty? I took them out. Aha! One of the contacts was very corroded. Maybe that was the problem! I cleaned that and put new batteries in and le voila: the heating came on. Success!
In the following days I hoped the thermostat would just work. It didn't! I think the remaining problem is that something about the timer is wrong. I have now got into the habit of switching it on 'daytime temperature' when I want it on and 'nighttime temperature' when I want if off. I'm not sure I want a thermostat in the long run! What about just adjusting the heating in the individual rooms? Using the knobs of the individual radiators?
Either way, the heating does work and I know how to switch it on. The details can be sorted later! The plumber is imminent anyway; that might change things. The house will be getting homelier as time moves along!