The most significant requirement is that the immersion heater be isolated from the mains supply should the primary thermostat fail with the contacts closed which would allow the water to reach a temperature in excess of 85’C · · · Separate safety manual reset cut-out · · For use in hard or aggressive water · · Can be used in standard water conditions · · Manufactured to BSEN60335-2-73 · · Two specific clauses aimed at eliminating the risk of boiling water