Chimney Cleaned for new gas fire?

Was getting gas fire installed at the weekend, the installer done a smoke test and said that there was no draw from the chimney, he suggested to get it cleaned. It has never been used before as it was a new house when I bought it, I also got a crow guard installed after I moved in. There has been a few birds hanging around my roof.

does anyone have any experience with this?

Can you look up the chimney (with the aid of a mirror if necessary) to see if you can see daylight at the top maybe?

the installer stuck his head up, but said he couldnt see anything, it was just dark i thought it was not a straight chimney, but i'll try myself when i get home

Chimney sorted, cleaned out with sewer rods, found 3 bits of newspaper rolled up.

Can anyone tell me if it is ok to use fiberglass as an insulator for a gas fire? this fire has cermaic back that comes to the front of the fireplace, with a flap that opens up. I need to insulated behind it??? hope this is clear