firstly, when you say you reset your boiler and it goes back to how it was before, do you mean it works ok then or does it continue to be in fault condition?
Richard is right, that a common fault on the baxi (and some other makes) is that the hot water diaphragm can perish but, you need to give more info to get the right diagnosis cos, there are many faults on boilers with similar symptons. Is the hot water demand light on constantly?, if so it could be the hot water spindle stuck out keeping the microswitch on, if no hot water light on(tap symbol) then it could be your timer is faulty or your room thermostat is faulty.
Stephen
September 2011