Central heating coming on all the time

Hi all,
Probably a similar subject sorry if this is. I have a problem with my heating system. The boiler is fine an old Potterton.. I replaced the old Potterton programmer with a new direct replacement EP2002 same backplate. I have noticed that the CH is coming on when only the timer is switched to HW. I have noticed the following :
Central heating pump spinning
Motorised valve (potterton) has 2 lights on it HW and CH and both are illuminated but the CH light is dimmer than the HW one but becomes brighter when I move the lever to the manual position.

I have checked the system with the CH and HW sliders both on but there is no difference to the lights on the valve.

I have checked the switch on the rear of the programmer ensuring it is in the horizontal position indicating a fully pumped system and even moved it to see if the problem changed and it did not.

I have a feeling that the valve could be faulty or the wiring on the backplate could be wrong (which I have not changed).

Any ideas anyone ?

It is the three port valve that needs replacing, It may only need a new head, which means no plumbing, but it would be good if you afford to change the whole valve to a new 3 port Honeywell valve IMO they are the best motorised valves, and easiest to maintain.