We have just moved into a victorian flat which has 6 original double hung sash windows and a have a couple of (probably stupid!) questions
1) 2 windows have broken cords. Is it ok to open them and prop them up while waiting to get the cords fixed? We want to paint the outside windowsill !
2) After unscrewing the latch in the centre the top wind falls on its own (not all the way) - does this indicate a problem with the cord as well? I always thought we could lift the bottom sash up and the top would stay in place.
re your second question, it could be that the weights need adjusting. Sash windows tend to 'get heavier' due to 100 years worth of paint, so they can tend to slither to downwards when opened. If this is the problem, the chap who fixes the cords should be able to adjust the weights so the windows are better balanced and stay put.
In answer to your first question, yes this should be fine.
You are right about the second point - the two parts wil have their own set of weights to counterbalanace the movement, and so should move independently of each other.
It's actually quite easy to replace the sash cord. There should be a removable pocket of wood at the bottom of the frame (perhaps painted over) where the weights can be accessed. If the weights are still there, it's just a question of carefully removing the beading keeping the bottom window in, and lifting the window out, tying a new bit of sash cord to the weights, and nailing the top of the cord back to the window.