Valliant Ecotec Pro 28 Boiler; F.22 Error?

I have noticed that for the past few days my Valliant Ecotec pro 28 has started coming up with the F.22 error. I have read other posts online about this error and how to fix it, but in all honesty I'm pretty confused!
Would anyone out there be able to write out a proper way to fix this?

Would be much appreciated!

Thanks :)