This is something important for you to know about hot water systems. If you had your hot water heater installed prior to 2013 this may be more pertinent for you.

By law, the minimum required temperature within a hot water heater needs to be above 55 degrees Celsius to prevent the growth of legionella bacteria.

However, this is too hot for general household use so a tempering valve is needed to lower the temperature of the water.

AS NZS 3500.1:2003 Plumbing and Drainage, Part 4 Heated Water Services Plumbing Code of Australia 2013 Part B2