Drayton Lifestyle LP822

It is two or three port valve stuck in close position. There's leave for manual operation. Exercise that leaver. Move it to open position and hook it (Honeywell), if doesn't work automatically.

So you get radiators come on when there is no demand for heat and you have only hot water on! But no hot water!! Synchron motor burnt out, or even three port valve stuck on heating only. Highly unlikely the two port valves "s plan", as that would mean the "heating two port valve " was stuck open and the other two port valve for the hot water was stuck closed, and a wiring conundrum. However ,recently I had a job that the customer had to have the hot water on to get central heating, and apart from a burnt out pump and faulty 3 port valve head, when changed out still needed the hot water on to get heating, this was in fact a very badly installed central heating system wiring center. The wiring was corrected and now all works properly. So unless an engineer ACTUALLY VISITS it could be a number of problems.

Morning Peter if your radiators are heating up when you turn your water on You could just simply have a wiring issue Alternatively your 3-Port Mid Position Valve could be faulty or stuck in the CH position https://www.toolstation.com/drayton-mid-position-valve/p52988

It does sound like the 3 port valve is stuck, it will have a manual lever on the valve that you can push from one side to the other, push it over and lock it in position, this does mean you need to get someone to look at it as it could also be a burnt out synchronous motor head or faulty wiring - hope this helps.