My brother in law has a problem with his sash windows - the bottom pane has warped inwards around 3 mills and can't be closed properly.
The windows were painted on the inside for a long time, but not the outside. He finally got around to painting the outside, and this may have caused the wood to warp (the window was new when I helped him install it).
I'm not sure how to fix it. Would forcing it into place and leaving it closed help bend it back over time, or is planing it a better solution?