A little gottcha for anyone with a S Plan heating system...
SWMBO had commented that the shower was not as warm as usual. Each time I tried it however it seemed fine. Given she does not have it anywhere near as hot as me (not as thick skinned I presume!), I did not give it that much mental attention at the time.
The other day I went for a shower and found it rather cold. A quick investigation showed that although the programmer was calling for heat, as was the cylinder stat, there was no call for heat from the zone valve. After investigation today, it seems the valve was getting a bit sticky, and the synchron motor could not quite drive it far enough to engage the microswitch. A bit of disassembly, lubrication, and waggling later and we seem to be back to normal operation.
Could well have been like that for some time, however during the colder months the water was getting heated anyway every time the room stat called for heat. Thus masking the fault. Now its getting warmer, there was less chance for the water to heat. Needless to say the programmer called water heating twice in the day, once early morning, and once early evening. it was after more radiator on time, and also after the main progstat had ramped up to higher evening temperatures hence running the rads more.