After a few attempts here are some pics so you get what i've been talking about. You can just see the spindle towards the left which should move along depending on what's needed HW, CH, HW&CH.
The big pipe right at the back which you can just make out in this one below is the one that is coming up from the boiler and is now hot. I had my hand on it yesterday when some air came up from the boiler and burnt me as it past through so i think if there is a blockage and it's not the motorised valve then the blockage must be around this area in the pic.
I believe the valve is a 3 port valve with a small leaver to adjust it from manual to auto. should the valve turn when either drawing water or heat because at this time the valve remains stationary.
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