Combine two Webasto's into one?

Hello everyone,
I'm new to this forum and would like to take advantage of this opportunity to ask a question.

My previous Webasto Top C (Diesel) has broken down. A friend of mine used a diagnostic tool to read the following error message:
NAK: Unknown negative acknowledgement code 0x45 or solenoid failure code 90
What do these error codes mean?

I would like to convert two Webasto (diesel) units into one, and I am now wondering if these units can be interchanged with each other (e.g., with a Webasto Top C/Z or E).
Do the differences generally only lie in the control software (i.e., only replacing the control unit)? Or are there also different types of glow plugs and combustion chambers, etc.?
I also read that there are TT models with 4.2 kW or 5.0 kW.
I would appreciate a response.

Best regards from the Lusatia region.
Greenling