Vaillant ecoTEC pro VUW 246/5-3 - Floor heating not working anymore (hourglass symbol appearing)

[spodoba]

Hi guys, sorry for the delay, I was out of town. I was hoping the issue will resolve itself, but I'm out of luck. Same issue still persists.
Here is picture more to the left:

When I turn on the heating nothing much happens. It seems flowrate through each of the 8 loops does not really starts (it is not 1.5 to maybe 3.0LPM). It's 0 or close to 0.

Here are the pictures of D40 and D41. It is pretty much the same every time. Hourglass symbol appears very early (aroung 30-35°C), so these D40 and D41 temperatures also do not rise much...

 

[Johntheo5]

What is the boiler pressure?, it should be 1.0/1.5 bar when cold.
Check that the "hottest" water is in the bottom UFH manifold as the flow is into the bottom manifold, through the loops and out through the top manifold.

 

[spodoba]

What is the boiler pressure?, it should be 1.0/1.5 bar when cold.
Check that the "hottest" water is in the bottom UFH manifold as the flow is into the bottom manifold, through the loops and out through the top manifold.

Pressure is fine. It is just in the middle, and it is like that for the last few years, so i don't think anything is wrong with it.

Water in the bottom UFH manifold is cold as it is on top, because it just doesnt have time to heat up. As i explained before, as soon as I turn on the heating, temperature rises to around 30 -35°C for a minute or two, and then hourglass icon appears, and it just stops heating. That is not nearly enough heat or time to feel any heat on the bottom of the manifold.
Thank you guys very much for trying, but it seems that this will be a job for engineer....
I suspect there might be a problem with diverter valve, or issue with erelax thermostat...