Eberspacher Hydronic S3 heater manuals and downloads are available to download at
https://www.butlertechnik.com/technical-library/hydronic-s3
specifically the installation manual provided by Eberspacher can be found at weblink below
https://www.butlertechnik.com/downloads/cms/7744/eberspacher-espar-hydronic-s3-d4e-d5e-cl-installation-manual.pdf
Unfortunately Eberspacher no longer provide printed versions of these technical documents within the heater set boxes.
Thank you, please let me know if you require any additional information