crazy problem, water pressure switch bore hole pump.

[BrownBear]

Dear All,
this is my first post here.

I will get straight down to the problem that has me really puzzled.

The house I am working on is not connected to the water mains, they have a bore hole well. The pump in the bore hole is controlled by a danfoss CS pressure switch which turns on/off the pump when the back pressure of around 5bar is reached.

The system has stopped to work all of a sudden after the long winter.
To describe the system
bore hole pump - pressure switch - inline water valve - branch to house - inside house bladder pressure tank - water pipes to sink/toilet/bathroom etc.
- inline water valve - straight pipe out to barn with simple tap on the end.

The crazy problem is that the system works fine for the house eg the pump goes on when the inline valve is turned open for each line.
As soon as the inline valve to the barn is turned off the whole system shuts down eg no water in the house!

Either the problem is looking me straight in the eyes and I am blind or something is terribly wrong?

Thank you for your help and suggestions in advance.
atb
David