Scorching above boiler heat exchanger.

[Mike Lamb]

This is a blind shot I took of a 20-year-old gas-fired boiler. I see scorching above the top of the heat exchanger. Do you think this is cause for concern?  Would a dirty exchanger cause this?

Edited October 30, 2017 by Mike Lamb

[Tom Raymond]

Where is the refractory insulation?

I'm betting what scorched is the adhesive left behind when the rats stole the insulation.