Be VERY gentle if using mole grips on a stuck pressure cap, or you may shear the cap off the circular plastic retaining ring above the threads. That ring is spot-welded in place, and holds the whole thing together. If you’ve already sheared it, clean up the parts, and get some duct tape ready. Re-assemble the cap, & carefully apply a two-pack epoxy glue only to the very edges of the ring and the shelf it sits on, or you’ll glue the whole thing together and stop it working properly. Use the tape to bind it all together and overcome the internal spring pressure while it’s setting.
The Fixer, May 2020