baxi 105e will not turn off?

My 105e will run on either hot water or heating/ hot water. When a hot water tap is run then turned off the system will not shut down. The temperature lights build up to maximum and stay on.Sometimes the heating display goes off but the lights for everything else stay on. I have to turn the system off then re set and re start the system again. This works until I run the hot water. Then the fault starts again.