Solar thermal water heating is a temperamental thing. Water weighs a lot, it expands when it freezes, and it can cause scaling damage to pipes when it boils. Solar thermal systems are wonderfully efficient, and some systems work just fine for decades, but even these need regular inspection. When a solar thermal system fails, however, it sets about destroying itself, and it has been clear for some time that solar thermal water heating is not the way of the future except for very low-end heat usage, like swimming pools.