How to adjust the temperature of the hot water
Keep your friends and yourself out of hot water. To make sure your water is running at a safe temperature, you may have to adjust the thermostat on your hot water cylinder.
What is a safe temperature for hot water?
Hot water should be stored at a minimum temperature of 60º C to avoid the growth of Legionella bacteria, but for safety reasons water in the bathroom basin, bath or shower should be below a maximum of 55º C.
The following chart shows how dangerous hot water can be to the tender skin of children and the elderly, so weigh up the cost of improvements to your hot water system against the cost of serious burns.
Temperature of water Time to cause a bad burn
66º C (150º F) 2 seconds
60º C (140º F) 6 seconds
52º C (125º F) 2 minutes
49º C (120º F) 10 minutes
To reduce the temperature between the hot water cylinder (60º C) and the
bathroom (ideally, 52º C or less) it is a good idea to have a tempering valve fitted between the two. As the hot water leaves the cylinder, the valve mixes cold water in, thus reducing the temperature. Another option is to install taps and shower mixers that have a tempering capability.
Adjust the temperature in your hot water cylinder
First, measure the water temperature in the hot taps. It is best to do this
early in the morning when the cylinder is at its hottest and before anyone uses any hot water. Turn on the hot water at the kitchen sink and let it run for 2 minutes. Hold a thermometer (outdoor, kitchen or bathroom thermometer) in the flowing water until the reading stops rising.
If the temperature is set too high or low, find the thermostat and turn it up or down accordingly.
Gas hot water heaters usually have a visible thermostat dial near the bottom
of the tank. In-line gas water heaters usually have a push pad on the wall for temperature control. Simply adjust them as desired.
Electric hot water heaters usually have either two panels screwed to the top
and bottom of the hot water cylinder or one panel along the side of the
cylinder. Thermostats are located under these panels. For safety, turn the power switch off on the cylinder, or at the mains before opening the panels. The thermostat can be adjusted by turning the central dial with a screwdriver. More modern units have a finger dial on the surface that is easily turned.
If the cylinder has thermostats on the top and bottom, this indicates that
there are two heating elements inside. Be sure you adjust both thermostats to the same temperature.