Boiler shuts down with thud

I have a Burnam V74 Boiler,about 10 years old,one pipe steam system.
I replaced the nozzle,fuel strainer,fuel filter,photo eye and electrodes.
I was having a problem that when the furnace turns off it makes
a thud sound. It doesn' t appear to be an explosion. Kinda sounds like
its sucking air in real quick. After changing everything it still is doing
it. The filter were all dirty as we ran out of oil a few weeks ago.
The thud noise seems to be getting worse. I appear to have a good
draft going. The fuel is coming out of the bleeder screw on the fuel pump
nice and clean. I have a full tank of oil. The only thing I have yet
to do it pull the side panel and top off and vacumn it out. Any ideas on
what to check next? I don't know what to do and really don't want
to call a repairman if I don't have to. Please let me know what
suggestions you may have. Hopefully I have provided enough information
on the boiler to help you ,help me!! Also, it ignites smoothly and runs fine
until shut down.....

Bill M
Mystic,CT

 

Is this noise coming from the boiler itself or from the barometric damper on the vent pipe? Does the burner shut down clean with no after burn? I would suggest a good brushing & vacuuming and let's see if it improves.

 

It seems like its coming from the pipe. I'll give it a good brushing and vacumn
tomorrow.

 

Cleaned the furnace yesterday. Gave it a really good brushing and vacumn.
A lot came off from the brushing. Sucked it all up with the sootmaster
vacumn. Filled a bag about half way. Also spent a good time chasing around
a gasket and the rope that goes inbetween the cast iron door and furnace.
What is the trick to getting the rope to stay in place? Took awhile to mess
with that one. After getting all back together it starts and shuts off like new.
Its a lesson in that I should have cleaned it in the fall when it would have
been on my terms and not its.....

Bill M
Mystic,CT

 

Use a thin bead of high temp silicone or a heavy coat of anti seeze compound under the gasket. Amazing what a good cleaning will do. isn't it. I'd bet since it got you once, it'll not get you again.

 

Thanks for the tip on the gasket Grady. You bet I won't let a routine cleaning
get me again.

Bill