Opensuse 13.x

edit the file:

/usr/share/pulseaudio/alsa-mixer/paths/analog-output.conf

change this:

[Element Speaker]
switch = mute
volume = off

to this:

[Element Speaker]
switch = mute
volume = merge

Opensuse Leap 42.1

above setting is already done, along with a lot of other, similar settings. Didn't find the proper place to fix. But alternate solution still works:

amixer -c 0 -- sset Speaker playback 100%

Probably best to put that in /etc/init.d/boot.local or similar