Apollo 50si boiler - pump runs when boler switch is set 2off

I have an Apollo 50si boiler which runs CH and HW. Programmer is a Potterton EP3002. All was working fine but for some reason one days the heating came on even when the programmer was off (no lights on it etc). There was also burning smell from it. I installed a new EP3002 and still same problem. One thing to note is that once the programmer is installed the pump starts even when the boiler is switch off (boiler is cold but tank full of hot water though). The mains is on but the boiler has 3 settings (high off and low) and this is set to off. So far I have changed the 3 way valve, V4073A, and programmer. Is it anything to do with the pump overrun switch? Maybe it is relevant to also let you know that I recently changed the pressure switch and all was working fine for a week (changed it as I melted it as I fired up boiler with system dry!!!). The boiler will fire up but the burning smell returns from the programmer. Any help would be appreciated. thanks