A problem with my heating controls?

I have a Potterton Suprima 60 with an EP2001 programmer fully pumped system with 2 MVs,the problem is that when the HW is on and the heating is off at the programmer the rads get hot even though the MV is closed,the same happens when heating is on and the HW is off.I have changed the cylinder stat to no avail,could it be the programmer at fault.
Thanks in anticipation for any help.