I have an old American standard hot water boiler that heats the house perfectly. But everytime the burner starts there is a big poof. Where should I begin looking to solve the problem.

 

Greetings and welcome....although I am not an expert or a tech I have had this problem. It seemed that the burner was spitting or spraying the oil into the chamber a fraction before the igniter sticks ignited the oil. They should work pretty much in sync with the help of an "electric eye" (not sure what the exact name of this part is) on the inside of the burner. I cured my big poof by changing the electric eye as I call it. However, while I had the burner off, I also changed the nozzle and igniter sticks and it ran like a bran new burner. In short I guess that big poof is the igniting of excessive oil in the chamber. I'm sure you will get some more expertise on this in the forum. Hope it Helped. I ran my Utica FHW for a whole heating season this way before I was helped with the solution.
-Bob

 

When was the last time the burner was serviced????? New nozzle ,oil filter, pump, electrodes set right and draft checked . You have to start with all of that first for a burner to work right. Moving the CAD eye wont do it. Also sometimes the transformer is going bad and after the motor is up and running the transformer will kick in and fire ,that will give you a bang when it lights. So be sure and check the transformer out also here. Post back with what you find out are need more info.

ED