My Vaillant boiler (ThermoCompact) has a fault (again) of f 33. I am painfully aware of what it is (the last time it cost me £300 to replace the fan) but it seems to recur too often (as it has now). Any ideas ?

David, January 2009

f33 faults on valliant first thing to check is the air pressure switch its on top of the boiler right hand side,you need a short bit of flexible tubing to fit on to it then you take one pipe off it,either blow or suck the pipe you put on it,if you hear it clicking its ok and then you know it is youre fan we have put 3 fans in three years and it looks to me as if they are puting in sub standard fans

Bryan gas service engineer, May 2010