New Pressure Switch won't turn off submersible water pump.

Wilde_37

HI
About 3 weeks ago I realised I had no water. When I checked the pressure in the shed it read at zero. I opened the pressure switch and manually activated it - it went up to 5.5 Bar (about 80 PSI) but did not cut out.   I bought a new Square D pressure switch and installed it.  But it keeps the pump running all the time - The pressure is still going up to 5.5 Bar and the pump is not cutting out.  (I turned it off after 5 minutes because I was afraid it might get damaged)
Thinking that the new pressure switch was faulty, I replaced it with another new one.  Same result.   I am now controlling the pump at the main switch as I am afraid to leave it running all the time.  This of course means that I have to manually turn it on and off when using water.  
The house is 18 years old and the pump is the same age.  The expansion tank is only 2 years old. The pressure switch is new (I have not adjusted it in any way from factory settings). 
I'd appreciate any suggestions.

Wearb

Perhaps get someone who does pumps to have a look. There might be a fault that would be missed by the untrained eye.
It’s no time to be without water.