I have come across internal concrete lintel cast in situe (spelling ?) with brick ties cast into the concrete to help support the external bricks, usually above a metal casement window or metal casement into timber frame, not the norm to see a straight corse of bricks unsupported as they normally have headers above the windows, I would be checking all other windows in the property.
Surveyor should have picked up on the lack of lintel tbh when job was measured. I used to check, by drilling with a cordless drill and masonry bit if in doubt.
It is usual to charge for a lintel, as an extra. But highlighted by the surveyor, but, before installation. Office would usually call to give a price, after looking at the photos. (which should be part of the survey and also best practice.) Pre instal photos also prove if the movement was there before installation. Probably depends how fair they play with the pricing*. It should have been installed before the new window/door. this would avoid any damage to the new frames and best fit..could probably argue that they have not carried out duty of care. Depends on route you want to take and *.
Anyone who is in the window trade should have a skills card, as you can see mine is for surveying and installation, it is part of the company’s basic requirements to be able to fit windows, there surveyor should have the card and the training, 100% the company’s fault and you should be paying zero, a call to Fensa or Certass should see you right, you need to find out who the company is registered with.
https://www.planningportal.co.uk/info/200130/common_projects/14/doors_and_windows/2 The relevant paragraphs before Thermal Loss....either 'Registered Competent Person' or if 'Unregistered', Building Control notification.
I think @simmytt is correct. They are responsible. Their opportunity to charge was before installation. Should have been picked up on. Ask for the work to be carried out FOC as it is their failure and responsibility. Also, I assume they did not instal any other window/door products? If so, they need to be checked also. If they don't want to play nice, then the Fensa and other organisations listed above need to be brought in to play.
Yes they appear to be Fensa registered and there insurance backed warranty is with QA, if you have no joy with the company then a call to Fensa should help things along, there are guidelines that the fitting company have to adhere to, lintels , fire escapes, toughened glass to name a few.
