The bulk would be enough to serve as protection from the heat, if that was your intention.
But what confuses me a bit is the right arm. Is there a real arm supposed to be inside that? If so it might be too short and thin. While the weapon design with the attached blade looks interesting, it should maybe be fitted below the armors forearm with a trigger to operate manually, or maybe make the overall arm a bit more bulkier like those deep sea diving suits.
And maybe his footing is a bit off, because I wouldn't want to throw a frag standing in a heavy armor like that.
Sorry if that sounds rude, .... but that's just what I think.

No, it's fine. I like critizism. Makes me look into my next drawings with it. I'm actually putting your thoughts into mind now that I look at the drawing. I did mess up on the footing and I knew that from the begining, so that is my bad.

That's good, because the overall idea is very interesting designed. The mask and the fuel units on the back make it look pretty cool. Just the arms were armored a bit too weak compared to the feet. Maybe using some kind of armored glove could do the trick.
Let's see with what you'll surprise your watchers next