Hot water at 60°C takes only 6 seconds to cause a full-thickness skin burn. At 55°C, it takes 30 seconds to do the same damage. Small children and the elderly are particularly at risk.
The Building Code requires that hot water for new systems must be supplied at taps used for personal hygiene at a maximum temperature of 55°C.
But hot water needs to be stored in a cylinder at over 60°C to prevent legionella bacteria breeding in the water. Any higher than 63°C though and you are just paying for the extra heat that gets lost ([see Cut your losses]).
The reduction between cylinder and tap is achieved by use of a "tempering valve", which mixes cold water into the hot. You are not required to have a tempering valve in an existing system, but if you replace your cylinder with a different type you may want to get one fitted.
We have received several complaints about tempering valves affecting shower performance. Plumbers tell us they often fit them to get past the building inspector, and then pull them out so their clients can get a decent shower.
However, there's no excuse for the valve not working properly, especially in new installation. Tempering valves can work if the system is designed right and the correct valve is chosen. But where a tempering valve is fitted into an existing system not designed for it, there can be flow problems.