No you do not. The end of the well, inside the boiler jacket it sealed.
You do not need to drain the tank. The robe goes into a thermowell. Its an easy install.
No you can install it without draining the tank , It's fairly easy to do-
I did not need to drain my tank. Mine attached on the top side of the heater.
I actually Have a kit on the shelf , It has the thermostat ,Knob and a new decal for the cover plate, decal with the SKU # and new rivets to attach the cover
This kit includes the stat switch, a new label indicating the temp range, and the bulb. My stat doesn't adjust the temp, it only cuts out at a higher than normal temp. It allows the water to get hotter than 120. It is the second one from PexSupply that I have installed and they both don't work properly, but it does cut out with the switch at the lowest setting so I am living with it. I am an electrician so I know it is installed properly.
The kit contained everything you need to complete the job plus new stickers for the temperature adjustment knob. It was a super easy to install fix.