Combustion driven oscillations are a common problem with boilers, water heaters, and furnaces. Sound is produced by the flame and is reflected downstream from the combustion chamber. The reflected sound waves disturb the mixture flow or equivalence ratio increasing the heat release pulsations and the accompanying sound produced by the flame. This phenomenon has been described using a positive feedback loop in prior work by Baade. The current report applies the feedback loop stability model to two boilers, which exhibited combustion oscillations. In addition, Baade's feedback loop stability approach was modified to predict oscillations due to equivalence ratio fluctuations.