I am not very familar with this plumbing and circuitry but you may have one or more than one problem. The electrical control for the water supply is not turning off the solenoids or the water valve commonly referred to as the mixing valve is leaking after it is supposed to shut off .Do you have a water supply that is from a well or is it from a city water supply ? Some wells are very clean and free of sediment and others are fairly dirty with sand, etc. The screens in the water supply hoses catch most of the small particles but eventually some debris gets into the mixing valve and leakage starts. Check the hose screens first but if that does not isolate the cause you might want to run a load of wash and after it completes the cycle unplug the unit. That will turn off the power and should prevent the solenoids on the mixing valve from allowing water to leak. If after that exercise there is still water slowly coming in to the tub chances are that the mixing valve is leaking after it normally supposed to be completely shut off. You should also check your hot water heater for sediment .Good luck and publish what you find.