motorised valves

Hi all, We have an old-ish open vented system from the late 1990s. The hot water has stopped working but not the central heating. Tracing the hot pipes, I notice that after the 3-way-valve the pipe into the cylinder gets notably cooler. It is reasonably hot just past they motorised valve but...

I have had a minor problem with my central heating for a couple of years now and finally got around to trying to work out what is wrong this afternoon. The system works but the central heating only heats up if the hot water is also requesting heat from the boiler. This means that when it gets...