Aquastat Relay replacement

Are some of them immersion (in the water type) or all of them in a dry well? He needs to know or will get the wrong one.

I used to do LOTS of boilers until I got specialized, then my plumbers took over. Saw a few that were screw in immersion type. That is why I let them do most of the water work. Don't mind the burners and controls.

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