What is the purpose of the plastic piece on a dielectric pipe fitting . I installed this fitting on a waterheater and damaged the plastic piece when I soldered the fitting . The fitting has no leaks but the plastic is melted does the fitting need replaced ? Is the brass part the key component in preventing the corrosion between the two dissimilar metals ?

Hi Sparky

It is the plastic that makes the nipple dielectric... prevents electrolytic effect.

Replace the dielectric nipple and then PRESOLDER any fittings before you install them onto the dielectric nipple.

Good luck!

Mark