Extruded volume gradually reducing

[sven1729minus1 0]

Hi,

after struggling for ages with this, I am out of ideas and would like some input from the experts on the printing defect I am experiencing.

Hardware:

- Ultimaker

- V2 hot end, recently upgraded after this problem appeared, hoping it would solve it. I believe to have assembled it correctly and according to the instructions on the Ultimaker wiki

- Bertho upgrade of extruder

- first used PLA from source on ebay but problem also persists with PLA from Ultimaker

- I have check that all belt drive pulleys are tight and also that the belt tension is good

Note: with the V1 hot end, this Ultimaker used to print nicely. Until this problem described below started appearing.

Software:

- Cura and PrintRun.

Symtoms:

1) When starting a print, the first layers tend to be ok, as the print progresses, the extruded volume is gradually reduced. The result is a print with very low density that is virtually see-through. Pictures attached.

This started during a very long print with large flat area (see pic) and has been aggravating since.

2) There seems to be gap between the walls and in-fill (see pics). I read that this is linked to belt not being right, but could there be something else. I am quite confident the belts and pulleys are good.

Usually I have to go through great lengths to remove the filament from the hot end after one of these prints. This occurred with the V1 and V2 hot end, so both tend to clog up, don't know why…

Normally I print at 200, but have tried up to 220 to no avail. Any ideas?

Sven