Question cannot get sufficient water flow thru shower head?

Showerheads don't normally get airlocks, sometimes if a seal isn't seated properly then it can restrict the flow. Have you taken the showerhead off and checked the flow available through the showerhose?
Also the flow will be a related to the water temperature setting as the power is fixed. If the flow is low and the temperature is correct then maybe one of the elements has gone open-circuit.
Good luck

Paul M
May 2009