balance spring

How difficult is it to replace a blance spring in a window? If difficult, who do I hire to do this?

peepm

If yours are the same as ours, it's easy.
There's usually one screw holding it at the top, to the window frame, and 2 screws on a return tab, securing it to the bottom of the sash...You need to raise the sash to see them. Be careful when undoing them, because if there is still tension on the spring, the can spin quite fast.
Once the screws are out, you can slide the whole thing out the groove in the sashes side. You don't need to take the sash out, though with some aluminium windows, it will come out freely at this stage.
Usually, you would replace both springs, even if only one is broken.
Putting the new ones in is just the reverse procedure, not forgetting to tension the spring, easily done by twisting the tab before securing.
Make sure you get the same size as the one you took out.
HTH
TM