Freaking out! Boiler pressure is going up?

I got home pressure was on 0. So i opened the tap to build pressure up. I have a potterton suprima 40. I turned tap off at 1.5. But pressure still went up to 2 2/4. I then turned the electrics off when it reached 2 3/4. I had already turned the central heating and hot water off, but that didnt seem to help. The pressure still goes up and down but has not reached the red mark of 3. There is an air sound around the boiler. As if it was deflating slowly. Never heard the sound before tonight. What do i do? Turning the tap water on for a drink makes the gauge play up!! Help!!!