Oil-fired furnace sight window repair

Question

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.

Answer 1

Using epoxy to hold the glass itself in place would be a bad choice, as the thermal expansion of the glass is different than the surrounding materials - this is why a clip is used rather than a more secure solution. The clip allows movement.

If you can figure out how it was originally attached, and repair that (perhaps with the aid of a welding and/or machine shop then that would be the ideal solution.

However, using epoxy to hold wire or a metal clip of your own design in place that holds the glass in place would also work out well enough.

Note: If the item that was holding the glass in place was rusted/damaged enough that it no longer serves its function, chances are very good that the heat exchanger is also nearing the end of its life, or already has pin holes, which would allow combustion gasses to enter the building. Do a thorough inspection.

Answer 2

There certainly are high-temperature epoxies that should do the trick for this (J-B Weld comes to mind, it's rated for a constant 500 deg. F but you should confirm that's higher than this part of your furnace gets).

But you say "my assumption is that the metal groove for the e-clip has degraded" -- does that mean you're not sure? I ask because to me this seems like an odd thing to wear out given that it's just holding a stationary piece of glass in place. Is it possible the clip popped out a long time ago and the groove is just full of soot or rust?