water heating thermostat

[i=p/u]

the hot water in my house is scalding nearly boiling, i have oil heating system and imersion heater that heats the water would there be 1 thermostat for both on boiler and where abouts would this be???? if you can help

 

[IQ Electrical]

the hot water in my house is scalding nearly boiling, i have oil heating system and imersion heater that heats the water would there be 1 thermostat for both on boiler and where abouts would this be???? if you can help

Each system should have a thermostat, sounds like something has failed, the immersion should have a thermal cutout.

 

[i=p/u]

well the heating hasnt been on today but immersion has..., we were changing immersion heater circuits/cables last week but didnt touch anything else. how would you test thermal cutout??? isit a simple change over????