I would appreciate some advice on this. We are an Energy company which does solar water heating installations. The installations usually make ue of a "Geyserwise Max" solar controller to control the electrical heating of the geyser, using time windows. Installation entails interrupting the power supply wiring between the Isolator and the geyser element and connecting this into the controller, which controls when the element can switch on and off. Please advise whether this requires a CoC.