I have a Quadra Fire Santa Fe I bought used. All seems well except for 1 issue. About 70% of the time if you set it on low the fire will go out. Seems better if it is fully warmed up(burned on med or high for a while and switched to low). I went through all the troubleshooting in the manual and video. Cleaned everything. Made sure the vacuum tube was clear. When on low it will stop feeding pellets. If I notice the fire going out and click to medium it will immediately start feeding again and work fine. Is there some kind of adjustment for feed time or something. I notice there is a small hole in the control box with a potentiometer behind it. Does anyone know what the potentiometer is for?