Tip: Worcester Greenstar Junior, Si & Ri Electrode Cable/ Connectors Connection 

Hi. If these don't get replaced every year, or at least every other year, these burner seals will stick to the Burner's top. I usually pull off, what ever I can. Then remove the burner from situ and use a snap off knife with a thin, snappaable blade, to scrape off, gently, any residue. Then use a fine wire brush to completely clean any remains. Hope this helps.

@BoilerMend aswell as that I was referring ro the electrodes rubber boots they stick to the electrodes