Ferroli Falcon II - Pressure valve problems? Please help!?

Hi, for months we've been topping up the boiler, and now it's every 2 days or so, and usually drops when I've just shampooed my hair in the shower! Anyhow today we paid £30 and put some leak sealing stuff in and let the heating run, which of course put the pressure back up to 3.0 then it cuts off so that's not the pronblem. I read on here somewhere about pumping something up to cure this.

We are under Ferroli Gold contract which I have found useless as I called them out and all they did was cut off the thing (sorry to be so untechnical here) where you could top up so we had to get our plumber out to put this back to how it was before. They also took 19 days from my first call. They said that this problem wasn't covered on my caresafe cover for which I pay £12.50 per month for so I might be cancelling this soon as I think I'll call them for another try but can someone confirm what they think the problem might be for us? Many thanks in advance, Gill