Honeywell aquastat L8124L install

I am planning to replace the erratic aquastat in an oil-fired furnace. I was able to get the exact replacement model-L8124L. Does it require shutting off water to the tank and priming after the install? I am assuming the thermostat will have to make contact with the boiler water for sensing the temperature. Also is it a DIY- I am fairly good at electronic circuits and confident to replace the wires.