does the gauge have to read below or above the red line to the right boiler?

The pressure should be set so that the pointer is just out of the red and into the green - usually about 1 bar. To get this pressure open the filling loop valve (to the left of the plastic key on a new boiler) and watch the gauge rise as you do so. Don't overdo it! If the pressure drops again then you have a water leak somewhere.

John
March 2008