2001 Allroad - air suspension - pump running

[vtraudt]

The pump is running quite a bit.
There does NOT appear to be a leak. Car can be parked on various height levels for days, without sagging.

Yet, the pump kicks in often and runs quite a bit.

Logged the 4 height sensors, and the reservoir pressure and reservoir valve and pump relay.

Notice that reservoir pressure is often ZERO.
After pump kicks in, climbs to only 4 bar (I am used to seeing as much as 16 bar, but certainly 10; pump has just been rebuild).
Then, without any movement on the 4 height sensor, reservoir pressure drops down to zero within less than 1/2 minute.

But also observed that reservoir pressure stays at 4 bar and holds forever.

There appears to be a leak.

How can I trouble shoot?
Narrow down where to look for potential leak?

Line/fittings from pump to reservoir?
Reservoir to valve block (if there is such a line)?
Valve block itself leaking?

[Leandre1]

I had simillar symptoms and it turned out to be a weak air compressor.
I tried rebuilding the compressor but it was too worn out.
I ended up replacing it with a used one from a 2005 Allroad.
Now the air compressor hardly runs and there are enough air stored in the reservoir to raise my car about 1 1/2 levels.

A spray bottle with soapy water is the best way to check for leaks.
Spray all potential leak points and look for bubbles.

[vtraudt]

Can a 'worn compressor' after rebuild leak the pressure out of the reservoir?
The compressor can raise the car fairly quickly one from level to the next (as a possible other indication that 'worn' may not explain the reservoir not holding pressure).