Brake pedal goes hard

[Humbucker]

Hi all,
I have had my2015 Passat Estate 2.0 TDI GT for a year now.
Its done 87000 miles and has full VW service history.
Over the winter comeing off a sloping drive after starting the engine the brake pedal is still hard and takes about 6 presses for it to work correctly.
This has appened about 5 times.
Last Saturday I had driven about a half mile and coming up to a roundabout and the brake pedal was hard and I was fortunate that no one was in front of me.
Its always been in the morning and it is always ok when coming home from work.
This morning I pumped the brake pedal till it was hard then started the engine and it took about 6 seconds before the brake pedal started to drop.
I tried the same thing coming home from work and as soon as the engine started the pedal started to drop.
Has anyone else heard of this issue with the B8 Passat or may have an idea of what is wrong and costs involved.
No warning lights came on which is un nerving when these cars seem full of sensors.

Thanks.

[Crasher]

Sounds like a vacuum line leak but this would normally cause a boost delivery problem.

[Humbucker]

Chees for that Crasher.
This morning it was 20 seconds after the engine started when the pedal sank.
In the afternoon going home its straight after starting the car.
Will have to take it in someware to get it checked out.

[Humbucker]

The fault is sorted.
Not a happy Bunny as VW new about this issue since June 2018 and they have not told customers about it.
It turns out its a none return valve in the vacuum pipe that gets stuck. £28 pipe but over £400 to fit as its below the intake manifold and the front of the car has to be removed including the inlet manifold. The good news is I have brakes and no turbo fault.
Below is the listed fault from VW.

Model 2015 Engine code CRLB
Release date 12th June 2018

Technical information
Engine: warning lamp for engine managment on after start, brake pedal briefly hard

Customer Statement
After cold engine start in the morning the brake pedal remains briefly hard
or
The engine warning lamp is on
or
The glow light is on
or
The engine has reduced performance

One or several of the customer statements can be reproduced
The following entries can be logged in the engine control unit (sporadic/static)
-P029900 Boost pressure below limit
-P256300 position sender for charge pressure regulator -implausible signal
-P00AF00 adjustment unit for turbocharger 1 jams

Technical background
A lubricant was used in production to install the vacuum hose. In case of longer
stationary period the lubricant can cause the non-return valve in the vacuum hose
to get stuck. As a result the non-return valve remains closed straight after engine
start this leads to a lack of vacuum for a few seconds ( In my case 3 miniutes)

[Crasher]

Sounds like a vacuum line leak but this would normally cause a boost delivery problem.

It was this TPI I was alluding to when I commented on the boost delivery as this is a well known issue but you did not mention it.