The NSW Code of Practice states that installing a Hot Water Tempering Valve is mandatory for all new hot water installations where there is a considerable change to the existing pipework. A Hot Water Tempering Valve helps to eliminate the risk of scalding. A plumber who does not install this valve is not only endangering those who use the hot water, but also himself due to the risk of litigation from such injury.
Elderly persons and young children are most at risk.
Over 90% of hot tap-water burns requiring admission to hospital occur in the bathroom, primarily from immersion in a bath containing water at an unsafe temperature or as a result of a young child turning on the hot tap whilst in the bath.

It just isn't worth the risk.
Ensure a Hot Water Tempering Valve is Installed on your hot water system.