Where is this ituated on a fabia vrs cheers:)

As stock, in the side mounted intercooler, which is in the offside front wing / front bumper area.

would this cause a boost problem?

No, as its a standard part. With out it, your car wouldnt work.

However if you mean, if its faulty, or the wiring is broke then yes, it could cause limp mode and other problems

If it was dead, vagcom would confirm it in advance before you starting ripping bumpers, etc off the car.

For the record, boost sensors generally are well made and rarely fail. It's usually something else like a leaky vacuum hose or dodgy maf.