Boiler surging noise

jesmed1 · November 19

We have two Weil Mclain WGO-5 oil boilers with Beckett AFG burners. Our regular boiler tech came in September to do the usual servicing and adjustment. When the weather turned cold and the boilers started running I started noticing a low-frequency surging sound coming from one of the boilers (the other one doesn't make the noise).

It's not annoying enough to call him back, but I am curious about what's making the noise. It's a low frequency "whuh-whuh-whuh" pulsing, almost chugging sound that occurs about once per second. I've put my mechanic's stethoscope (a long screwdriver) on every major component (oil pump, blower motor, combustion chamber housing, vent pipe) but the pulsing sound doesn't come through the screwdriver. The sound is most noticeable when I put my ear near the barometric vent damper, so it sounds like a combustion instability inside the chamber. I thought maybe I'd be able to see a pulsing flame if I put on my welding mask and opened the flame inspection door, but the part of the flame that I could see appeared fairly stable.

So I am curious to know what's causing it. And secondarily to know if it's problematic enough to be worth a callback. I don't want to waste our tech's time if it's not worth the trouble.