Propane heater with yellow flames and roars

We installed a comfort glow 50k vented propane heater for my mom. (thanks for all the help with the installation questions). The other day she said it started to roar...make a lot of noise (it does not have a fan). so she turned it down without looking at the flame and it seemed OK. I went up yesterday and there was a fair bit of yellow/orange flames. I took the burner out and cleaned it and the orifice. But neither. really seemed that dirty. The combustion area seem good....no soot. Today it happened again and this time she looked at it and said there was a lot of yellow/orange flames. She is using a 120 gal tank and it is at 30%. Up to this point (2 months) it seemed to be working OK. Because we bought it used I am wondering if I should change to orifice just to be assured it is the right size. It has been in the single digits here if weather can be a factor. She did change propane tanks a month or so ago but has had a fill with the new tank. Thanks for all your help. Julie

Like Bob said- it sounds like "fire in the hole"
sometimes slightly closing the air fuel shutter will eliminate this (once you are sure there is no mis-alignment...)

I will check for alignment. Here us a link to the owner's manual .page 34 shows the burner set up

http://desatechgasheater.danielcada...er-cgr65bpa-cgr65pa-cgr50bpa-cgr50pa-cgr35pa/.

.the set up doesn't seem like it would allow for much movement but anything is possible. I don't see an air shutter. Where would it be? Thanks Julie

I check the alignment and it seems good and the bracket the orifice gets mounted to is very rigid so it would be unlikely that it has moved. I would say that this is a dedicated propane as there is nothing in the owners manual about converting. I had the orifice checked and it is the right size. I am going to reinstall the orifice. Anything else to consider? Thanks again. Julie

When I went to reinstall the orifice I realized that the heater was not level...it sat about 1/2 inch lower on the orifice end. Any chance that could be my problem? We did level it. Julie