How do I stop water coming out of plastic pipe on my Triton Opal Shower?

I fitted a new shower head to my Triton Opal shower but it seemed there was not enough pressure to push the water through the new head. After trying to adjust the new head to a different position, water started pouring out of a plastic pipe situated just behind the outlet pipe. Is there a part broken or is there some kind of pressure relief valve that needs resetting?