Normally closed thermostat that opens when tempreture is reached. It is marked '80' so we guess it's 80 degrees. Alos written on the part is 54n0976.
80°C Normally Closed Manual Reset Thermostat Thermal Temperature Switch NC
80°C Normally Open Thermostat Thermal Temperature Switch NO
80°C Normally Open Thermostat Thermal Temperature Switch Flat Terminals NO
Joblot 11 x Joule TZC-D-00000J-Z Dual Boiler Thermostat 25 - 65 degree C 16A