As a follow-up, it sounds like it might be the 3-way valve being faulty (from Google research).
If I turn off the power to the system and move the manual lever, I can feel the resistance / hear the motor turning. However, this only starts from about 25-50% of the movement - i.e. the first bit...
Hi all,
I have a typical hot water / central heating setup based on the Honeywell Sundial Y Plan - 2 Channel Programmer with mid-position valve and an old dial room thermostat.
The hot water is an unvented system, but I don't think this makes any difference for the problem I'm...