Back in the Summer, I found that my hot water was no longer getting hot, and after a bit of fault finding, found that although the hot water zone valve was opening correctly, it wasn't operating it's internal switch to start the pump and light the boiler, so in effect nothing was happening and the water stayed cold.
It was a Honeywell valve, and when I took it apart to have a look at it, I found it was made in 1976. So had probably been working for around 36 - 37 years in a hot airing cupboard.
I looked at alternatives, then spoke to a plumber friend who advised me to get another Honeywell as he so rarely had faults with them.
Naturally the Honeywells are the most expensive of the valves I looked at.
Regardless of the make, they shouldn't be failing that quickly though, but I thought I'd just mention my experience.
Ian
ps interesting to compare the insides of the original 1976 and the new Honeywell zone valves - better insulation & electrical connections and ability to remove the mechanicals without letting any water out on the new one, but otherwise - identical. I suppose a good design doesn't need that much tweaking!