How to spot an obsolete immersion thermostat

After the death of Rhianna Hardie, the baby who was scalded because of a broken immersion heater thermostat, many people ask me how to tell the difference between an obsolete thermostat and a more modern fail-safe re-settable type.

This is an obsolete model - note that there is no reset button or indicator

This is the re-settable type - the circular recess between the terminal screws contains the re-set button which springs out if the high limit is breached - you just then push it back in to re-set

This one has a re-set light - when the high limit is breached the temperature setting dial pops out and the re-set light  illuminates. To reset just push the temperature dial back in.

If you are not sure and wish to check your thermostat safely remove it and put it in a pan of boiling water - any re-set mechanism should activate and a check across the terminals should reveal no continuity.