The good thing about the heat pump I've got is that it's also surprisingly quick to heat up. If you do run out (I never have, but I experienced the speed the fi

The good thing about the heat pump I've got is that it's also surprisingly quick to heat up. If you do run out (I never have, but I experienced the speed the first time it was turned on when it was installed) you can go and press the 'Boost' button on the controller and you will have 50L in 20 minutes and a full tank (mine is 315L) in 3 hours. The system also heats the tank to at least 60 degrees C at the sensor point (about 2/3 of the way down) at least once every 24 hours and then has a tempering valve on the output for safety. That way you don't have scalding water at the point of use, but do have lots of hot water available and no issues with Legionella bacteria.