BWR stability analysis is a challenge for the nuclear reactor dynamic in-depth analysis. In order to understand the solution manifold of the differential equations describing the stability behavior of a BWR loop in more details we apply coupled codes (nonlinear system codes) and an advanced physical based Reduced Order Model (P-ROM) coupled with a bifurcation code complementary (RAM-ROM approach). In the framework of these investigations we could interpret some system code results in more physical terms. Particular nonlinear solution types with operational safety relevance are stable and unstable limit cycles because in these cases 2-3 stability states coexist and small amplitude oscillations and large amplitude oscillations could occur spontaneously under a control parameter variation. In the paper we demonstrate two (partly) novel local bifurcation analyses results predicting the existence of large amplitude limit cycles. Because of the operational safety relevance of these oscillations and our experience that system code algorithms sometimes predict not the proper oscillation amplitude we recommend to start the BWR stability analysis with a procedure which is suitable to clarify the (possibly complex) stability landscape by local bifurcation analysis and plan on the basis of this knowledge the coupled code runs.