Lg heater help

So today I lit the pilot on my lg heater just like usual. Started up the generator, fired up the escape then turned the heater from pilot to on position. As soon as I did that a large flame shot out the bottom of the heater and stayed lit until I turned the knob to off. I tell ya I almost pooped my pants when it happened.
Anyway needless to say I did my job with cold water.
When I got home I pulled the lg and propane tank out to inspect. It fired up no problem. Turned it on no problem. I let it...

Lg heater help