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 to 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, 55 degrees Celsius is too hot for general household use so a tempering valve is needed to lower the temperature of the water. A tempering valve reduces the risk of scalding.
What is a tempering valve?
A tempering valve is a mixing valve that is installed between the hot and cold pipe work. It mixes the hot and cold water together to reduce the temperature of the water before it enters the house or fixture.
AS NZS 3500.4:2015 Plumbing and Drainage, Part 4 Heated Water Services Plumbing Code of Australia 2016 Part B2