Can't change tcp_keepalives_idle

Hi,

Change tcp_keepalives_idle in postgresql.conf from 0 to 300 , then pg_ctl reload but it stays with the old 0 value.
Tried restart and it did not work. PG Log says it was changed.
Reset_cal marked OK, but no real change ( ins how)

-[ RECORD 1 ]---+-----------------------------------------------------
name            | tcp_keepalives_idle
setting         | 0
unit            | s
category        | Connections and Authentication / Connection Settings
short_desc      | Time between issuing TCP keepalives.
extra_desc      | A value of 0 uses the system default.
context         | user
vartype         | integer
source          | session
min_val         | 0
max_val         | 2147483647
enumvals        |
boot_val        | 0
reset_val       | 1800
sourcefile      |
sourceline      |
pending_restart | f

Thanks

Danny