declare @t table (id int, nr int, [text] varchar(2),  val1 varchar(1))
insert @t
select 1, 1, 'aa', 'A' union all
select 2, 1, 'bb', 'A' union all
select 3, 2, 'cc', 'B' union all
select 4, 3, 'aa', 'C' union all
select 5, 3, 'ab', 'D' union all
select 6, 4, 'cd', 'E' union all
select 7, 4, 'rf', 'F' union all
select 8, 4, 'rt', 'F' union all
select 9, 4, 'qq', 'G'

select t.*
from   (
       select nr
       from @t
       group by nr
       having count(distinct val1) > 1
       and    count(*) > 1
       ) d
join   @t t
       on t.nr = d.nr

OUTPUT:
id          nr          text val1
----------- ----------- ---- ----
4           3           aa   C
5           3           ab   D
6           4           cd   E
7           4           rf   F
8           4           rt   F
9           4           qq   G