Double-glazed sash window goes "twang"

Just over three years ago I had the whole house (Victorian terrace) double-glazed and the old sash window was replaced by a beautiful and expensive modern sash.

Over the last few months, when opening the bottom panel I have noticed a sound in the lower right-hand side of the frame that sounds like a spring going "twang", and the window seems to catch on something as I slide it up. The "something" isn't preventing the window from sliding up, but I am wondering what it is, and whether it will jam eventually. It is worst when I open the window for the first time of the day. (I open it several times a day as I have a cat that wants to go out and come in all the time!)

This window was very expensive and installed under a grant - there is no way I could have afforded the work myself, so I am anxious about tinkering, in case I break anything. Any double-glazing experts who can tell me what it means and what, if anything, I should do?


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if it is a modern one it probably has a spiral balance with a spring in it (old windows used balance weight, pulley and string).

sounds like the spring or string is catching on something. Do you have any reason to suppose it is due to poor workmanship or faulty materials? If so you could complain to the supplier.

see if you have a leaflet or anything with the maker's name on it.

if it has spring balances they are reasonably easy to replace as maintenance parts. I think last time I bought some they were less than £10 each but you have to get the right length and weight. A local window specialist (if he does old houses and not just plastic windows) will probably be able to fix it.

Look at the sides of the frame where the windows slide in grooves. Mine have a spring push in/pull out thing that is used when fitting the balances, it has to be pushed right into the frame the rest of the time or it would catch (but mine are Amesbury-type balances which you are unlikely to have).