PXE boot now requires F12 intervention

I have been using SCCM  in testing for about a month.
Everything has been going fine up until the other day.
When i send Images to machines via Task Sequence the machine boots into PXE, but before it goes in it requires users to press F12 to enter the network service boot.

I haven't changed anything for this to start appearing
Is there anything that has happened, or something i can do to change this, as it defeats the whole remote deployment concept.

Cheers