Theoretically, this cycle could continue indefinitely without a problem. However, there have been accidents due to incorrect installation. The immersion heater could be used in locations where there is no guarantee that the water in a malfunctioning heater would be replenished. Therefore, to comply with the basic requirements in the IEC 60335 series of standards a thermal cut-out has been made a requirement of the new standard.
If installers have stock of the old product these are safe to use, but they should change to the new product for all future purchases.
Source
Electrical and Mechanical Contractor
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