One additional data point: on my heat pump the economy setting for hot water production starts heating once water cools to ~42C (truly, a universal answer) and

One additional data point: on my heat pump the economy setting for hot water production starts heating once water cools to ~42C (truly, a universal answer) and heats it up to ~55C. As for anti-legionella, once a week there's a cycle where the top setpoint is raised to 65C.