From April 2004, members of the Association of Manufacturers of Domestic Appliances (AMDEA) will only provide electric immersion heaters that meet BS EN 60335-2-73.
The change is to ensure that new immersion heaters all have a built-in cut-out that will operate if the water in the tank reaches 98°C when the thermostat fails. Until now, only a thermostat was fitted and the safety back-up relied on the fact that the immersion heater was built into a vented water system that would eventually heat up the cold water cistern, bringing the problem to the attention of the occupant.

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.