the furnace guy was just here a few days ago doing maintenance. He adjusted
the flame height by eye, no instrument. Today I suddenly noticed a loud
rumbling both when the burner starts and stops. I experimented by rotating
open the peep hole door a little to give it more air, and the rumbling stopped.
I believe I do see how to adjust the air intake, which I want to do until the
furnace guy comes back. It looks like a collar that is rotated around the same
axis as the motor shaft. The collar is to the left of the whole burner assembly.
1) Does the boiler rumble because it has too much air or not enough air?
2) Would it be bad to leave that peephole door ajar for a few days, instead of
adjusting the air intake? It would let some cold air come down inside, but is
there any other problem?
3) Why would this noise have suddenly developed? Is it that something went
wrong inside the works?