Given that such things are remarkably twitchy about water pressure, shutting off at the first hint of trouble, I wonder if your hand was lower down than the shower head in normal use, or if or does not work when something else on site, like a washing machine or dish washer, is also running. Given that pressure, flow and temperature are related, it could be that it works OK for a tepid shower but not a hot one, or on some settings of a multi-hole nozzle and not others.
Mornin' all, after a bit of investigation I suspected low water pressure. Two other showers in the building worked o.k. though. Those two were different makes and models. The weather here is very hot and there has been no rain for some days. I imagined that local people would be using garden hoses. Indeed the B&B owner had his garden hose in use at the time that I was testing the "faulty" shower unit. After the hose supply was turned off the shower performed perfectly. Low water pressure was the problem after all.
Today I gave my customer four longer anchor bolts to install his new Solar shower by the new hot tub location, it won't be much use without the hose pipe.
Just to help it do its job the outside tap has a hot and cold supply with a thermostatic mixer.
