Has anyone had an issue when removing the drain plug on the metal pipe assembly underneath, came to replace the thermostat today and the drain plug wouldn't come out subsequently cracking the braze and now a massive leak, been to two weld shops who can't weld it as its brazed, has anyone swapped this out or had this problem before

Find yourself a plumber, if their any good they will own the torch to braze and repair our pipe in 5min, or pop into a diy shed and get your own a brazing kit.