Sometime last winter I noticed that my CH thermostat had changed its behaviour. Instead of being on for ~10 minutes and off for ~20, it would run the heating for ~40 seconds, then off for ~2 minutes. It was as if it somehow lost its hysteresis. Given that it's an all-electronic system (Drayton RTS1) I suppose it's possible that, e.g., an electrolytic capacitor has dried out (or leaked). Is this a common problem?
I'm not that worried as it seems that the RTS1 is still available cheaply and as it clips into the backing plate I'll not have to put screwdriver to connector, just plug new gubbins onto old plate. If I can get the old one out... It hangs on the upper-right corner; I suspect the old chap who used to live here, and was a bit less proficient at DIY than he seemed to think, put conduit over the wire after it was in place and didn't leave enough room to lift the body off its locating lugs. We'll see when I get a new one to compare.
There was a moment of panic when I apparently didn't get it plugged back in correctly after trying to prise it loose, and the thermostat didn't switch on at all. Fortunately a second attempt got it working again so I won't have to spend the next few days wrapped up warmly.