screwdriver operated isolation valve

[steedmanj]

I had to switch off the cold water to replace a high pressure valve on my header tank using a screwdriver operated isolation valve, but now that I have switched the water back on, there is insufficient pressure, so that my electric shower is showing "overheat" and is therefore not heating the water. There is insufficient pressure for the garden hose to work (connected to an outside tap). Is there something I'm not getting with these screwdriver operated isolation valves? Am I supposed to turn a specific number of times? In what direction?

 

[steedmanj]

Thank you if you have taken any interest in my previous post. I have now solved my problem on my own and no longer need the help requested.

 

[thelondontapcompany]

Isolation valve

How did you solve the problem could you let us know for future reference

John