my vaillant boiler wont start?

hi can any1 help me my vaillant boiler is coming up with the error code f20..on looking at my boiler i must have broken a part of the pressure sensor...ibought a new 1 and it still came up f20 so i thought its got 2 be the pump.....5hrs later ive just checked it again and now its saying f7 ...on checking error code i saw this now means fire detector defective.please please can any1 help me to solve this problemo because if its not the pump and something else thats silly i would be grateful for a little help!!thanx Rebekah