Okay, maybe someone here has an answer... maybe not... but I'll ask...
I have the same 'hot water sensation' - only, it's in my butt cheeks, near the anus... The easiest way for me to describe it is in 2 descriptions... Hopefully someone can relate and respond...
Description #1:
About a month and a half ago I went in for an angiogram. They used a new closing procedure on me which left a balloon like thing on the tip of the puncture location. While attaching that balloon thing, I felt the warm blood inside my body shot from my vein and around the inside of my leg... at the time, it felt like it was on the outside of my body but when the procedure was said and done, no sign of exterior blood (they did not wipe or vacuum the area I felt the warmth). That warm blood feeling is what I feel in my butt cheeks, closest to my anus.
Description 2:
Gas... Ever lay a silent one? A very stinky silent one? The kind that, as it comes out, you're thankful a match wasn't nearby... That's the warmth behind it... Just not centered correctly for it to be gas.
Hope someone has an answer...