Responsibility for lintel breakdown.? My house was built surrounded by 1903 and had its window replaced...

My house was built surrounded by 1903 and had its window replaced with UPVC D/G window about 12 years ago (now out of guarantee).
There is unconditional lintel failure above the longest window (about 8 feet) and show the classic zig-zag pattern within the brickwork above the window.
My interview is should the window company be completely responsible for sorting out the problem?
They could argue that the problem be probably there earlier the windows be fitted (unlikely as the buiding would already be 90 years old at the time).
The infirm wood windows would hold been pretty hefty things as the style of the house is monied Edwardian near ornamental brickwork and huge wood bannisters and newel posts.
I am all the same to meet the company so I don't know their impulse but I can't imagine it self easy.
I don't know how much it will cost but it is with the sole purpose three windows artificial (others are shorter) and it will cost them a lot smaller number to do than me.
They have made a locked building unsafe.
How do I stand legally?
Plumbing. contained by canada, how do they find...
Answers:    The lintels are what is supposed to get the the weight of the brick, not the window. You will have no luck contained by going after the window installer. Especially 12 years after they be installed. The lintels have former for some reason. As another post mentioned, phone for an inspection by a structural engineer. They will be capable of tell you the exact end in and offer suggestions for remedying the problem.
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Can you not claim on your builings insurance? lift it you have cover