Why does my hot water cool in my solar cylinder even when I am not using hot water?

Solar hot water cylinders are generally heated 50% by solar energy and 50% by an alternative heat source such as a boiler or heat pump. The solar content occupies the lower half of the cylinder whilst the alternative heat source heats the upper half. On a day where the solar collectors are subjected to an increased amount of solar gain, the domestic hot water will be hotter as there will be good stratification of the cylinder. However, on a day with less solar gain, the water at the lower half of the cylinder will be cooler which over a period will destroy the stratification and cool the entire contents.

The information provided here is advice only - if you are not happy to check your product, please contact a heating engineer to assist.

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