The interior surfaces of heat exchangers used in domestic hot water systems are particularly prone to fouling or complete blockage due to the accumulation of sediments, scale and mineral deposits. In many locations, mineral salts and other impurities may be present in the potable water supply and fouling may occur if the heat exchanger is not routinely cleaned or flushed of accumulated matter. In small residential installations, however, this is not practical due to the associated costs. In response to this need, a passive back-flushing system was designed that allows heat exchangers to be routinely back-flushed many times a day. The action is a normal operation of the system and does not require user intervention, external power or controls to function. During back-flushing mineral deposits are washed out of the heat exchanger and flushed from the system. the operation of the device and documents the results of accelerated tests undertaken to verify its operation.

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