Navien NR-240A Combustion Fan Noise

GaryC

Been in our home about 18 months (2011 built home). The first year the Navien was quiet, mechanical room is in the garage. This summer the combustion fan (top left corner with the cover off), makes several rpm adjustments during the recirc phase. It will kick on, then ramp up higher and then a third ramp up with an extreme high RPM. I have talked with the Level 2 techs on the phone and sent an video recording with audio to them and they said it is normal. I can't buy that when last year we never heard the unit, now we can hear it from the 2nd floor master bedroom. I've changed the flow sensor and all 3 thermistors, which I decided to do because it was low hanging fruit so to speak, (all four parts cost 45.00 dollars. I have a spare motor on hand because I am wondering if it is failing internally.

Jamie Hall

Have you made quite sure that the combustion air flow is completely unobstructed? The exhaust? The fan and its controller are trying to provide enough air to the burner, and there are obstructions...

GaryC

Intake yes, have not looked at anything on the exhaust side. Thanks I'll give that an inspection as well and repost later.

GaryC

Update, Intake has no obstructions, unable to verify exhaust since it is vented to the roof above the 3rd floor and the HOA does not allow me to climb up on the roof.

I did go ahead and change the combustion fan and it was caked with fine dust build up similar to what I've seen on forced air furnace blower fans (consistency of flour). So it runs a little quieter, but maybe now that my ear is tuned to listen to it, I can't objectively say whether it is like it was a year ago.

I did blow out the old fan and it was loaded with dust build up, but will keep it as a spare now that it is clean.