They definetly appear to have ' blown ' . As stated they will be under warranty , and first port of call is the original installer, as Fensa do not operate a ' guarantee ' . You will only be able to contact the aftermarket ' Warranty ' if the installer has gone out of business.
Fensa ( and Certass ) is a trade body for self certification , ensuring all members conform to supply and fitting windows to current building regulations, they do not offer any guarantee or warranty for the work done , that is supplied by the installing company , and then registered with a third party warranty company ( which is a proviso of both Fensa and Certass schemes membership ) who will then continue the guarantee if the installing company ceases trading.
As for retailers hating this problem , yes its true we do , but not because of the customer , but because we have to go back and carry out remedial work at OUR cost , work that need to be done through no fault of ours. Looking at those pictures it is clearly a manufacturing issue and NOT an installer issue , BUT the installer is always your first port of call as that is who fitted them , and that is who your contract is with