We are renting a house and have been using the coffee urn as a source of hot water for tea/coffee for the last 2 months. I don’t know what it was used for prior to. Religious people have been here bevire us. All I know is that I don’t want to incur the expense of purchasing a new urn just for the duration of Pesach. Our pesach wares are miles away at the moment. So I buy only what I really need.
No need to kasher it.
The way you would kasher it, if it was required, is by filling it with water and heating that up.
But it sounds like you’ve been doing that all the time, so it’s technically kashered over and over.
Additionally, people do not put Chametz in a hot water urn. So no need to kasher anyway.
So it’s all good. Enjoy.