Recently, we found a Viessmann CI2 399 model that had been installed about 2-years.

The complaint was "The fan runs, but the unit doesn't fire and goes into lockout". F.380 and F.971 were some of the main recorded codes.

In actually, the burner was igniting, but flame was failing when the combustion fan increased speed.

 

Upon inspection of the combustion fan and burner interior, bugs and dried leaves were found.

 

 

Using a small brush, a vacuum, and dry nitrogen, the blower wheel was cleaned.

The burner required blowing (from the outside-in) the mesh while shaking the burner, trying to get the dust and debris to exit the section between the inner and outer burner.

Be sure to not damage the outer mesh, wear gloves as the mesh coating is sharp.

 

The burner will index with the welded seam on the opposite side of the ignitor and sensor assembly.

 

Combustion chambers should be inspected and cleaned on an annual basis.

 

If there are intake screens, these should also be inspected for any build-up of pollen or dust.