So, a new noise has developed with my forced hot water furnace that I suspect is 'not good'. After the oil burner is going for a few mins, I'm hearing a 'phaser' ping like sound from the unit. Continues for a moment after the burner cuts off, then is quiet until the next burner cycle. There doesn't appear to be air in the system, it's normally decent about self bleeding after I manually bulk bleed it, got a new over-pressure valve and air bleed this spring, at that time the expansion tank was good. Seriously, it sounds like it's auditioning to do effects for a cheap TV space Sci-Fi. "PHEEEeeew" with a decrease in frequency and volume each time. Sounds like from somewhere around the top of the unit, maybe the exhaust/chimney, harder to hear around the unit, more noticeable upstairs where the roar of the burner is muffled.
Two fans on this, outside air intake, and primary burner blower, both driven off the same motor. Sound doesn't happen at start up, it's not till the burner has been flame on for a bit, persists for a min after the burner and blowers stop. The more I listen to it, it's almost like a needle drag on vinyl... bah.
Not sure what your gun burner brand is but if it's a Beckett I'd start by checking the motor fan for debris. Have you adjusted the igniter probes and changed the gun burner nozzle any time you've owned it? When's the last time you changed the injector nozzle?
Beckett burner, noise doesn't seem to come from the fan area or be related to RPM, but will look. I normally limit myself to the electrical and water plumbing bit of the system, the burner/furnace itself I leave to professionals. Looking at the service notes, electrodes last replaced in 2019, furnace was downfired from .85 to a .65 nozzle at some point in the past but was prior to 2019 and I don't have the logs for then. They may have been putting new nozzles in every service as the spec is noted each time, but not specifically mentioned as replaced so I'm assuming not?
