Hi,either the tank thermostat is faulty or the hot water motorised valve is stuck. The thermostat should make a click sound when turned completely up then down.
The motorised valve has a spring lever that should be closed/stiff when hot water is off
Hi, yes this is one of the safety valves opening due to either a failed pressure reducing valve a failed hot water temperature sensor..
If the 3water being released is hot then it is most likely the hot water tank temperature thermostat. If the water is cold it is most likely the pressure vessel is flat (it may have an internal pressure vessel(on some megaflo)or faulty or the pressure reducing valve is faulty