Baxi Boiler - The pressure dial is in the red at 3?

Hello,
Our heating hasn't been working for the last 24 hours, and we have had no hot water.
When investigating the boiler, the pointer on the pressure dial is in the red at number 3.
I know that when it is at 0, you need to turn a little switch thing until the pointers back in the green. But this does nothing when the pointers all the way at 3.

Can any one advise me what to do?

Thank you