boiler runs fine only with door off

jtelectric

I am having a couple problems with an older oil fired steam boiler.The boiler has a removable 3"x5" cast iron plate with the observation port glass on it on the door of the chamber.1st problem is the glass is broke there is just a hole in the plate seems easy enough to fix  but i`m not sure what kind of glass or where to get it.Do i go to a glass or plumbing supply house?2nd problem is the boiler works fine only when the whole 3"x5" plate is off.It dose not matter how long i run the boiler for as soon as i install the plate I get a flame about 4" shooting out the observation port.I cut a peice of sheet metal the size of the glass an installed it to try to temporarily fix this but when i install this i get a puff back comming through the fan.Not sure why it only works when the plate is off?

Charlie from wmass

boiler needs service

the chimney , flue pipes, and or boiler passage ways maybe clogged. Please for safety call a service tech in to properly diagnose the issue hands on.