Vaillant ecotec plus 630?

Hi.
I have a vaillant ecotec plus 630. I get the F.22 error message atleast once a month this year, which means that I have to keep topping it up with fresh water from the valve. Last year this never happen and I only got the boiler installed at the beginning of last year. I have wet underfloor heating downstairs and rads upstairs with one room having vertical designer rads which sounds as though there is a mini water fall inside it (trickling water noise). Can you help me?