My Hotpoint DF62P does not complete cycle ?

After replacing the wash pump impeller the unit will only complete one cycle then it stalls on the second use.
With the left hand side panel removed I can watch everything happening during a test cycle, spurred on by slowly advancing the timer and it seems to work OK.
However, when asked to do a real cycle, it hangs up. The wash cycle commences, the soap tablet is dropped into the sump.and water is heard to spray around, the spray arms rotate and it does wash the dishes. The programme stalls half way through the wash cycle and the discharge pump runs continuously and does empty the sump. When clicked to advance, the timer does advance occasionally but no second phase of washing or rinsing takes place. On reaching the end of the cycle the unit does not switch off and the drain motor runs on and on. I have to switch it off at he wall.
I have considered changing the isolating switch on the wall to a double pole switch to fool the unit into thinking it has been disconnected (it would be easier than pulling the unit out and unplugging it) but that would not be a fix, it might just be an effective way of resetting the unit. There was a smell of overheating when the drain pump had run on for a bit, but it is still working.
I would welcome any advice that would sort this pilot induced failure!