I have a Heatilator GNRC33 in propane and rear vent and standing pilot. It's about 10 years old. When new and for the first 5-6 years it worked great with pretty yellow flames and looked like a real fireplace. After six years or so the flame size started to diminish to a smaller, bluer flame. This year the flame is completely blue. I don't see any ghosting or lifting but just a blue flame. I opened up the glass and blew everything out. I pulled the logs and burner and blew it out. I closed the air shutter on the burner tube a little. It was opened all the way. Nothing has really altered the blue flame. I can try closing the air shutter more but I think it's odd that the fireplace worked fine for many years with the shutter in the full open position. Is there any other possible cause of blue flame?
THX> Eric
THX> Eric