What is wrong?

This sounds very much like the cylinder in the unit is scaled up. The only way of finding this out is by removeing the shower head and see what type of flow you have. If the cylinder is scaled up in the unit, then I am afraid it is more cost effective to purchase a new shower unit. If you are confident in removing the cylinder in the unit, then take it out and fill it with malt vinegar, leave it for a couple of hours and then flush it out thoroughly with water from the kettle or de-ironised water. Replacement cylinders can be purchased, but they are quite expensive. I am not sure what the manufacturers warranty period is on Trton units, if it is still in warranty, then get back to the people who installed it and they will be required to remedy the problem. I always use Sadia, they are more suited to hard water.

Richard
October 2012