At times knots can slip through your fingers while winding a warp and you find them later during weaving. Kerstin explained a nifty way to fix them which requires no further repairs once the cloth is cut from the loom.
Oh no! A knot in the warp!
insert a repair end into the same heddle and dent as the warp end with the knot
pin the repair end into the cloth, hang it over the back beam and weave about an inch and a quarter or so
cut the end with the knot out and toss it over the back beam out of the way
weave until the original end is long enough to bring back through the heddle/dent and pin it to the cloth (white pin)
weave an inch and a quarter or so and cut out the repair end
Remove pins and clip all loose ends and continue weaving. The cloth is repaired and no further work is required once you cut the warp from the loom. Tack, Kerstin!