rust inside fireplace insert

[Gazing in Wonder]

Hello,

I cracked a brick at the end of last winter's season. I've been burning this year with the cracked brick, and it's been fine, but I finally got a new brick, so I tried to install it today (damn thing doesn't fit, but that's a different question). I was surprised to find rust behind the back brick. I've had this insert for a little over a year (installed in late November, 2011). When I cleaned it out in the spring, it seemed quite dry. When I checked it out this fall before burning again, it seemed quite dry. I can't imagine how this could have happened. Could it have come this way? Is it something I need to fix? It doesn't seem like there's serious pitting, but it's a fairly substantial amount of rust, mostly on the back. Perhaps I'm getting rain down the chimney? Thanks for any advice.
GiW
I edited to add pictures. For the last three, I reached my camera around the back of the insert, where I can't get my eyes. Is the liner supposed to be that color?

 

[webby3650]

The liner turns that color as it gets hot, it's normal.
Unless you have seen wet ashes, then I'd say everything is fine. I'm not sure if the rust is normal, I don't usually see a new stove without the firebrick.
It's probably just from condensation.

 

[granpajohn]

Gazing, I did in fact find rust on my insert a year or 2 ago. And found it was rainwater leaking down the chimney liner. Not much, and no real damage done, but I was quite annoyed with it at first.
My liner is insulated, so it was easy to find moisture in the ceramic wrap before it all evaporated. And my rust was up on the outer top shroud; not inside the unit.

I determined that only rarely did it rain hard enough to leak, and I had certain suspicions, but it turned out that the mortar crown was about shot. I rebuilt it with a modern polymer concrete, and it's been dry since. Also looks better and more durable. Glad I did it, and feel a lot better.

Anyway, I recommend (this Spring) that you go up there and look that chimney over good, with leakage in mind. You may find something.

 

[Beer Belly]

The dealer that sold us our insert suggested we keep a box of Arm and Hammer....or Rid Damp in the stove on the off season, or keep the door ajar to allow for air flow to avoid moisture build up

 

[Highbeam]

That's one of the reasons that fireboxes are so thick. It is a corrosive environment. You know that paint is not going to withstand those temperatures so you have bare metal mixed with water from combustion mixed with heat mixed with corrosive gasses from combustion. Sufrace rust is expected but deep cancer is not. Some people only get a couple of years from a single wall (steel) chimney pipe.