Given that shower isolators are prevalent and a handy means of switching at the bathroom; there are probably many that give satisfactory service, I suggest that the problem is with limp wristed installers or the switch location being covered up with excess, thermal insulation. The ones that simply switch pressure pumps are probably most troublefree, having a lower current rating.

Jaymack   

Well, I went to CEF (only buggers open this week) and picked up a Click isolator - no 2 screw option though, only a single screw for each terminal. I fitted the thing but am forecasting that it won't be long before I have to go back and fit another. Shower is a Mira jobbie but I couldn't find the KW rating label on it anywhere. All I know is that it was fitted roughly 9 months ago.

Well, I went to CEF (only buggers open this week) and picked up a Click isolator - no 2 screw option though, only a single screw for each terminal. I fitted the thing but am forecasting that it won't be long before I have to go back and fit another. Shower is a Mira jobbie but I couldn't find the KW rating label on it anywhere. All I know is that it was fitted roughly 9 months ago.

A resistance measurement of the elements might have given a fair indication. There does seem to be some corelation on the few I`ve tested, enough to hint at an estimation anyway.

In fact I did the measurements of a couple of 3 element types and noted some kind of corelation as being "within the parish" sort o` speak. The reason I was doing it was to calculate a reconfig to put elements in series to get an idea of the likely resulting KW for a lower power in line water heater jobby.