My Valiant boiler may have an issue with the heat exchange.. not sure... but when I open the inspection/pilot light cover, flames want to come out! What is causing this?? Thanks!

My Valiant boiler may have an issue with the heat exchange..not sure...but when I open the inspection/pilot light cover, flames want to come out! what is causing this??? thanks!

Start by inspecting the draft for the flue gas. It could be obstructed causing flame roll out.

Most likely either the passages in the boiler are plugged or there is a restriction in the exhaust piping.

Thanks guys! both of these answers were very helpful! I cleaned out the grating and it appears to have fixed the problem....