Slightly off topic as I havent a clue which flux was used but I was called to a warranty job where the customer couldnt pressurise the system boiler was in about 7 months, installer had used copper from the boiler to below the floor then Hep2O elbows under the floor, he had over fluxed his fittings and it had run down the pipe to the Hep2O elbows and had rotted the grab rings and they had popped off , there was hardly anything left of them , use flux sparingly only use what you need