That is what you have to do but you can't set a DOCVARIABLE from a field so
you have to use SET and REF fields

e.g. put the following at the beginning of your document

{ IF { MERGESEQ } = 1 "{ SET previousZimmer_Nr "{ MERGEFIELD
"Zimmer_Nr" }" }" "" }

Then at the point where you want the page break

{ IF "{ MERGEFIELD "Zimmer_Nr" }" = "{ REF previousZimmer_Nr }" "" "<put a
hard page break character here>" }{ SET previousZimmer_Nr "{ MERGEFIELD
"Zimmer_Nr" }" }

All the {} need to be the special field braces you can insert using ctrl-F9.
You can probably get rid of a few of the double-quotes, especially if
Zimmer_Nr is always numeric.

A minor problem when using { MERGESEQ } is that it's not set to the current
record number when you preview, only when you actually merge, so the preview
does not necessarily work how you might expect.

Alternatively, if you are executing the merge from VBA, you can consider
using MailMerge events and directly altering the Mail Merge Main Document
when you detect a change in Zimmer_Nr

Peter Jamieson

The following macro will separate a catalog type mailmerge into separate
tables when the data in the first field changes.

' Macro to create multiple items per condition in separate tables from a
directory type mailmerge

Dim source As Document, target As Document, scat As Range, tcat As Range
Dim data As Range, stab As Table, ttab As Table
Dim i As Long, j As Long, k As Long, n As Long
Set source = ActiveDocument
Set target = Documents.Add
Set stab = source.Tables(1)
k = stab.Columns.Count
Set ttab = target.Tables.Add(Range:=Selection.Range, numrows:=1,
numcolumns:=k - 1)
Set scat = stab.Cell(1, 1).Range
scat.End = scat.End - 1
ttab.Cell(1, 1).Range = scat
j = ttab.Rows.Count
For i = 1 To stab.Rows.Count
   Set tcat = ttab.Cell(j, 1).Range
   tcat.End = tcat.End - 1
   Set scat = stab.Cell(i, 1).Range
   scat.End = scat.End - 1
   If scat <> tcat Then
       ttab.Rows.Add
       j = ttab.Rows.Count
       ttab.Cell(j, 1).Range = scat
       ttab.Cell(j, 1).Range.Paragraphs(1).PageBreakBefore = True
       ttab.Rows.Add
       ttab.Cell(j + 1, 1).Range.Paragraphs(1).PageBreakBefore = False
       For n = 2 To k
           Set data = stab.Cell(i, n).Range
           data.End = data.End - 1
           ttab.Cell(ttab.Rows.Count, n - 1).Range = data
       Next n
   Else
       ttab.Rows.Add
       For n = 2 To k
           Set data = stab.Cell(i, n).Range
           data.End = data.End - 1
           ttab.Cell(ttab.Rows.Count, n - 1).Range = data
       Next n
   End If
Next i