его is what? If it’s кастрюля, then it should be её since it’s feminine.
Also, if it’s кастрюля, the verb should be ставить instead of класть. There are some hard-to-explain rules for this in Russian

An interesting thing about colloquial English language and its lack of precision here... We would say 'put the porridge on the hob', although we mean 'put the saucepan on the hob'... I'm sure there's a child out there who took that literally at some point.