Hi Alex – this is my third attempt at a reply. I really don’t want to be critical but the forum app isn’t too great.

I have a 42C (2005) and the Owner’s Manual shows those switches as:

18 – spare

15: – “Heizung” – heating.

I’m not going to attach the photos I took but if this finally goes through I’ll send them as a follow-on.

Hope that helps.