Viessmann Vitodens 100-W: Radial Fan Air Intake Port Deteriorating / Wearing

WoodsCourtHeating

Hi Viessman Experts,

We have a Viessmann Vitodens 100-W propane furnace and the Radial Fan NRG118 air intake port deteriorates to the point where it drives F4 errors and has to be replaced. Also noticed fouling on the it's burner interface flange. Seems like the burning propane flame is somehow backing down the input channel which I can't imagine is intended. Please see the photo's below.

Any thoughts on why this is happening would be greatly appreciated, we are now on our 2nd fan replacement in 6 years!!!

Thanks, Paul