Why is it Warm???

The on-going standoff with the radiator has reached a climax.

When I came home today and it was warm, I knew something was wrong. I've been putting off asking for help with the radiator, but this was clearly go time. I had to place a semi-frantic phone call to my grandma.

Gma: Hello?
Me: Grandma! Grandma! It's me! I have to ask you something! Grandma! It's warm in here.
Gma: Ok...
Me: No, like, it's really warm in here. I think the radiator is... ON!!!
Gma: Yes. I turned it on today.
Me: Oh. Ok... but.. but... butbutbutbut.. It's making noise.
Gma: Yes, they do that.
Me: Ok. But this is like a hissing noise.
Gma: Yes, that's the kind of noise they make.
Me: Yeah, but I can like, hear it hissing.
Gma: That's what they do.
Me: Are you sure??!!?
Gma: Yes.
Me: Oh, well, I mean.. I don't know...
Gma: Is it leaking?
Me: No.
Gma: Is it making the house warm?
Me: Yes.
Gma: Ok, call me if either of those things change.
*click*