How hot should my water be? Cylinder tanks and bath water explained...

As part of our standard snagging inspection we check the heating and plumbing, so often our customers ask us about their cylinder tank and how that relates to how hot the bath water should be.
Most modern cylinder tanks that you'll find in a new build house will have a temperature dial similar to the one shown here. The purpose of it of course is to determine how hot you want your hot water to remain. Now at this stage you may be wondering about Legionella so its worth briefly explaining about that and how your cylinder tank combats it.
Legionella and other bacteria are actually always present in the water supply, but the bacteria breeds the most in  warm stagnant water between 25° to 50°C, With this in mind, of course the bacteria stays dormant below 20°C and does not survive above 60°C. 
So does this mean you have to set your cylinder tank above 60°C?...
The answer is no, because every time the cylinder tank comes on via the timer, even if you have it set to below 50°C, it purposely raises the temperature above 60°C and stays like that for an hour. This explains why at certain times of the day your hot water is hotter.

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So what about my bath water?

To avoid scolding in the bath, the building regulations have stipulated that the temperature of hot water coming out of your bath should not exceed 48°C.
The way in which plumbers meet this criteria is installing a TMV2 fitting underneath your bath. This is a thermostatic valve that restricts the temperature below this 48°C threshold.
So on a practical basis this explains why your bath hot water is (and should) be noticeably lower in temperature compared to your other taps.
Of course, like anything in new-build construction, short cuts are made so we quite often find that they do not install the thermostatic valve and the hot water comes out the same as the other taps.

For more information about the range of checks we carry out click here