Rinnai fan blows flame off burner in high demand operation

johnnayb

I recently serviced our Rinnai R75LS--vinegar flush and removing a small museum collection of moths from the fan. Now it seems as if the fan is running too strong; when under high demand the unit will "flame out"; like the fan is blowing too strongly?? I have error code 10 and 12 from before the cleaning; this issue doesn't create an error code which is odd, because it can create quite a blow back and feels like the unit may damage itself as it can cavitates strongly. Here's a video showing the flame under light demand and slightly higher. The blow-back is more pronounced with even higher demand (more flow or higher temperature set point).https://youtube.com/shorts/oYqg1x7AEzE. Any suggestions or questions most appreciated!

Slimpickins

Make sure your vent is clear and if so. You need to pull the burners and use at least 100 psi of air press, and blow both directions. A code 10 is restricted air flow and a unit that age needs the burners serviced. As far as knowing how to do it, youtube is your friend.

SummitMechanic

I would recommend having a combustion analysis done on your unit. It sounds to me that your gas valve/venturi were at some point adjusted when it had restricted air flow and will no longer supply enough for proper combustion. This would definitely choke it out in high fire and cause a "violent" sounding pop when it fires and a warble sound and vibrations while running in certain situations.

johnnayb

Problem solved.... I order and installed a new fan. To my disappointment the problem persisted. On closer inspection, I realized that the tang on the back of the fan housing was not properly seating (the heater is in a difficult spot to service without removing the adjacent toilet). I am guessing the inaccurate fit was causing less air flow, and thus the fan over accelerating. Palm to face. SummitMechanic; thanks for your help!