Cracks around upstairs windows

[Househelpplease24]

We had our old timber frame windows replaced with uPVC almost 3 years ago (July).

Recently we have noticed cracks around some of our windows - some horizontal, some vertical but 2 diagonal ones on upstairs windows. We originally thought it was plaster but then DH found gaps at the top of the external frame which should have had foam in. Company have returned to resolve the missing foam but can not help with the cracks.

Home insurance won’t help as they don’t fit their profile as subsidence.

A surveyor/structural engineer could do a visual inspection but wouldn’t be able to remove the fascia outside of the only crack visible externally.

I feel a bit helpless, I’m not sure what the next step is to try and find someone to resolve this. Is it a builder job?

It maybe that upvc is 'harder' than wood so creating a block. Very common too see this.

For example if you have a crack in your wall mortar and you fill it with cement or resin you will find it gets bigger year by year cracking into the brick but if you leave it it simply remains the same.

That occurs because (especially in seasonal climate like the uk) houses and the ground expand and contract with temperature shifts and rainfall levels. Cracks open naturally with this movement. If you spot the crack when its wide and stuff it full of something hard when it contracts back it has no space to close but the house can't stop contracting and whatever is softer (usually the brick) has to give.

I assume wood has more flexibility than plastic as wood expands and contracts heavily itself in line with the same weather changes.

If its just the mortar cracked its likely fine, most old houses have these expand and contract cracks in the mortar around windows or doors, they can be pointed with lime usually (lime might crack again under pressure but should not damage the structure) if they are causing a damp issue.

I'm not a architect though and haven't seen it but from what you said that would be my 'assumption'.