A leaking press joint is almost never the fault of the machine or the jaw. It is always the same seven mistakes. Know them and you press it right first time.
The seven mistakes
Pressing the wrong profilePressing a TH fitting with a U jaw seems to work, but the deformation is wrong and the joint fails sooner or later. The correct profile is always marked on the fitting itself. Not sure? Profile guide.
Not deburring or calibratingThe burr cuts the O-ring, and the leak only shows up months later. Here is how to do it right.
Not marking the insertion depthWithout a line you cannot see that the pipe has slid back during pressing. Half the insertion depth means half a joint.
The jaw not square to the fittingPressing at an angle gives an incomplete contour. Place the jaw straight over the collar of the fitting and let the machine do the work.
Interrupting the press cycleMachine released too early or battery flat halfway: the fitting looks pressed but is not fully pressed. An interrupted press is not finished off: cut the fitting out and press a new one. Viega requires this too in the approval for Profipress G.
Wrong insert sizeA 16 mm fitting in a 20 mm insert does not press tight. Profile and size must both match, for example TH16 for a fitting marked TH 16.
Reusing or shifting a fittingOnce pressed is final. Pulling off, twisting or re-pressing a pressed fitting in another spot makes it leak. Made a mistake? Saw it out, new fitting.
What is not a mistake: the small ridge that a two-piece universal jaw leaves on the fitting. That is cosmetic, the seal sits inside on the O-ring. As long as the machine completes its cycle without an error message, the joint is good.