New insulation sleeves as the old foil/polyurethane were beginning to crumble.
It did mean taking the boilers out but gave me the chance to remove the heating elements and inspect the boilers.
No scale just dark from filtered water, a quick dip in citric for elements to clean & inspect , a check with resistance meter= all OK.
Although the elements have teflon seals, I do wrap the threads with PTFE, it makes for smoother installation and prevents scale forming on the threads (making removal difficult)
