Flame in Burner Bed Tube

Hydrotherm

I have an older hydrotherm boiler in my house. Tonight I noticed a weird noise coming from the boiler in the basement. When I inspected the boiler, it appears that a flame was occurring inside one of the tubes of the burner bed. I turned the heating system off at the thermostat. Gave it a few minutes and turned it back on. When it fired up, the problem didn't reoccur. Is this something that randomly occurs or sign of a larger problem?

JUGHNE

My first guess would be dirty burners, low gas pressure or low draft from the chimney. FWIW

EBEBRATT-Ed

What @JUGHNE said plus one of the burners may be knocked out of alignment

Hydrotherm

Thanks everyone