Brake Booster not holding vacuum

[Trex4x4]

So I've finally replaced a faulty BCS only to find the brake booster is not holding vacuum.
Doesn't seem to be a common problem?
Or
Is it an overlooked fault?
Sends the car into limp mode as there is no boost (vacuum at the BCS).

 

[Old.Tony]

It's not a common fault at all. That said, it has happened before. Replacing the brake booster seems to be the fix. I'd be absolutely sure it's not a vac hose first, because vac hose is a lot cheaper than a brake booster!

 

[Trex4x4]

Bolt in the end of the hose and boost like never before...

 

[Trex4x4]

Well the strangest thing happened, thought I would do the service manual tests so I pulled the check valve, blew both ways thru it, reinstalled it and put the hose back on, tested the booster, drove it, can't fault it, no more limp mode.
Maybe the check valve was stuck?
Still makes a noise like a mobile phone vibrating in the booster but drove it for 1hr different ways and happy dayz...