First what was not causing the problem of CH not switching off when CH only required
I had fitted new, all of the above without curing the fault and the boiler is 4 years old.
Boiler wiring for pump overun in the garage beside the boiler was not as per the boiler fitting instructions. it seemed to have been rigged to save wire so I rewired it correctly but this did not cure the fault. I then put in a new airing cupboard junction box to replace the cramped rats nest installed by the house builders 20 years ago. To do this and to ensure separate and direct wiring to the pump, I used a wiring diagram provided via an e mail by the Drayton Help Desk. ( Make sure that you get the diagram that includes boiler pump overun.) See attachment
This diagram was very helpful and very clear
After all this I did not cure the problem. So I ordered and obtained another Drayton 3 port valve actuator and valve from a different source.
This second new actuator is now fitted and the system is working normally so PROBLEM CURED.
if you have a Drayton 3 Port Valve and your central heating will not switch off when either of, or both, your programmer and room stat are off then the actuator on the valve may be faulty and require replacing.
In my case I can only summise that the micro switch in the new actuator bought 6 weeks ago that supplied power to the orange wire was sticking in the on position and this kept the boiler firing up. I am not taking it apart to confirm this as its going back for a refund tomorrow.
Thank you all who contributed to this thread it greatly assisted in building up my knowledge.
ED07-1 BIFLO with LWC3 and Pump Over Run Boiler.pdf