Screw extract heat exchangers

Good morning in the round, after the fan blower was successfully installed, the poti of the inside outside engine is apparently defective and the climate control flashes (sometimes someone has an idea) now also the heat exchanger seems to be incontinent. There are traces to recognize, it stinks and sticks. The screw in the middle was quite loose. I have now tightened these hand-resistant. Has this ever worked with someone?