Listen to the Bus: Ambient Sounds & More

Hello everyone!

I want to connect to the bus of my central heating system and 'listen in' (from the control unit to the user interface).
Using an oscilloscope, I measured that the bus is running at 67 kbit/s. In 'listen only' mode, I don't see any messages. In normal mode, I can sometimes display a maximum of one message, after which the bus crashes and the red LED on my CAN232 device lights up.
Can anyone help me? I would be very grateful for any advice.
Sure, here is the translation of the text from German to English:

'Best regards,
wagnersepp1511'

What voltage levels did you measure with the oscilloscope?
And what kind of transceiver does the CAN232 have?

Does the CAN232 device introduce additional termination resistance to the bus?
I've experienced that before as well; it can be difficult to identify with SMD components. With an 11 or 29-bit error, the adapter shouldn't crash immediately.