O
Ockyvines
You're right, that's why I get so wound up when I see blokes spreading it on like they are creosoting a fence.True but even if you just flux the pipe, flux residue can/does still trickle down the inside of the pipe, I try to use fluxite on gas pipe as its not as harsh as say Laco.
When you turn a tap on the whole bath or basin is filled with green sh*te but you know that loads of it will have solidified inside the pipe to start eating away in the future.Because of the reaction between copper and steel, the poor radiators are the main things to suffer if not chemically flushed.
Excess flux is just that -excess and does nothing to help make the joint