A thermostatic mixing valve or tempering valve are devices that blend cold water and hot water to produce a constant temperature supply. The valve has a thermal element which expands and contracts to offset shifts in the hot and cold water temperatures;
According to the plumbing Standard AS/NZS 3500:4 water cannot be delivered to sanitary fixtures at a temperature higher than 45 or 50C. On the other hand, water inside the tank has to be stored above 60C to prevent the growth of Legionella. Setting the hot water unit to 60C and allowing for a temperature drop over the run of pipework might get you close but its tight.
To resolve this grey area tempering valves were made mandatory for all new builds, bathroom and ensuite renovations, and for replacement hot water system and piping installation. They are not required, however, for hot water system upgrades or replacements.
Views vary from plumber to plumber on what constitutes a replacement / upgrade and what constitutes replacement and piping installation so we recommend you speak to your plumber about your particular installation prior to commencing work as TMV’s and associated pipework do increase the install cost significantly.