Analysis of air intake in deaerator feedwater pump

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As shown in the figure below, the inlet and outlet pipeline system of the deaerator feed pump is as follows: bottom of the soft water tank (water level at 1.5–3.2 m, water temperature around 50–60°C) → butterfly valve → Y-type filter → pump → check valve → butterfly valve → deaeration head of the deaerator (the height difference between the deaerator and the pump is approximately 25 m; the heat source is steam generated internally, with a maximum internal pressure of 0.05 MPa). The feed pump operates intermittently, with water flow starting when the water level in the deaerator is low and stopping when it is high. At present, after the pump has been running for about 12 hours, gas is generated inside the pump, resulting in insufficient water supply capacity; normal operation is restored after the gas is removed. In my opinion, it is likely that when no water is supplied to the deaerator, some of the steam from the deaerator enters the pump through the pipes. Could everyone help analyze where the cause might lie?