I have an 20+ year old oil burner and a tankless boiler/furnace. There is a small round (2-3" diameter) window above the burner that lets you see the flame, I assume as an aid to tuning the burner.
After noticing a slightly smoky smell in the basement I found that this window was leaning outward from the wall of the furnace. There is an e-clip there as well. My assumption is that the metal groove for the e-clip has degraded enough that it can't hold the window in place any longer.
Is there an easy and safe way to repair this myself? I was thinking of some sort of high-temperature adhesive but I'm not sure what to use.