Suggestions to repair dishwasher please?

Hello, we have just bought a second hand dishwasher ... Hotpoint Aquarius DF61. The program has started but the dial has stopped at quite a short point into the cycle. If the dial is turned the cycle proceeds (completely unsure yet if it is doing what it should be when you randomly turn the dial in that manner). We don't think it is the heater because we have tried turning it to rinse and the water did heat up. Any suggestions please