I live in Europe and have a gas furnace that heats the water in my hot water storage tank. I would like to add a backup electrical heating element to the tank that I can turn on if our furnace ever breaks, if there's a disruption to the gas supply, etc.
I believe this port pictured below could be a G 6/4” pipe thread which could accept a standard electrical heating element.
To proceed, I imagine I would need to shut off the furnace, shut off the water supply, drain the tank, open the port, confirm it's 6/4" pipe thread, screw in the new electrical heating element, refill the tank, and then turn everything back on. Does that sound right? Are there other considerations I'm missing?
Edit: I located the manual