call National Shower Spares, they can usually diagnose most faults, visit web www.showerspares.com, try mearsuring the water pressure with another tap running, this will give you the maintained pressure which is what the shower needs, usually a min of 1.0 bar will be sufficient. does your shower get hot at all, or are you expecting more flow than the shower can actually deliver ??, if it is getting hot, measure the flow from the shower head, you should get around 4-5 ltrsmin at an normal shower temperature, hope this helps.
GARY
May 2008