My heating engineer, who is very good and always does a good job,
fitted a new 3-port valve in the airing cupboard last week. He
replaced the Danfoss with a Honeywell. The Danfoss has lasted 15
years. He explained how these valves work and said that it was always
better, if possible, to have the hot water switch off AFTER the
heating, because this guarantees less wear on the valve due to the way
the valve positions itself when the hot water is switched off. Even if
one has the central heating on and it is then turned off, it's a good
idea to switch on the hot water briefly, even for only 30 seconds, so
as to reposition the valve beneficially.

MM