Vitodens 100, Question with Damper.

Lash

I have a Vitodens 100-W built in 2007 installed in 2008. My Vitodens replaced a Penn WV-76 (Pink) Boiler. My natural gas consumption drop substantially, (by 2/3). It took three of us to carry the Penn out of my basement, while I was able to carry the Vitodens down myself. I am satisfied with it quietness and efficiency. I would purchase one again although Vitodens are not common in my area, so service technicians who are familiar in its operation are scarce. I am a professional engineer by trade and have learned to perform the basic maintenance functions. I’ve had an F5 fault display which the manual indicates “Burner blocked” and, cause “Faulty air pressure switch” (PS). The PS was checked out as OK. The boiler tubes and radial fan blades cleaned. On startup, I was still receiving an F5 fault. I could tell by the sound of the radial fan that something was blocking the air flow. What I found blocking the air flow was a closed “check” damper located within the air passage after the radial fan. Removing the radial fan exposes this damper. A finger push on the damper door freed it so it would swing freely. This had occurred twice (F5 fault), within a week, with the same problem: stuck damper door. I sprayed WD40 on the door frame. It has been several weeks with zero degree weather and no problems. My question is what caused the backpressure that forced the door to close so tight? The only thing I can figure is it’s from an “explosion” in the boiler probably during shut down. It had been windy but I don’t see how the wind could work its way down to cause the damper to slam shut. Any ideas you may have would be helpful. Thanks. PS I have found this website helpful.

CMadatMe

Flapper can be replaced. Part # is 7374 870 and was a known issue to happen back then.