I have a slight rumbling on the 120DPW Quiestside condensing boiler. When the flame ignites. Maybe a slight delay in the ignition I don't know. Im a Rinnai guy. We got heat /HW but this rumble slightly shakes the unit for 1/2 second. Tech says not unsafe. Anybody have any ideas?
We install Quietsides all the time, awesome piece of equipment. We started installing them about 6 years ago and have found the rumbling you describe on a few installs. The issue seems to arise from the vent termination that is provided with the Quietside. If you used the termination kit that came with the Quietside, I would start out by adding a piece of pipe (12-18") to the 90 for the air intake. If this stops the rumble, you have a few options. Let me know if this works and I'll give you a few recommendations.