boost gauge reading zero

just noticed it on the way home tonight the boost gauge is reading zero,
gave her a bit of a push and it moves up a very small bit,
I can still hear the turbo spool up and the DV lets go no problems, the needle in the dial is ok, because it does the start up and shut down seq ok
going to have a look tomorrow in the day light and see if anything has come loose just wondering if anyone has any ideas on what to look for

would it be the vaccum hose on the back of the gauge

I think the problem is with a vacuum line.

cheers will have a look