Water restrictions in some parts of the country result in the water pressure in the mains being lowered to reduce leakage and preserve water resources. The reduction in pressure in the mains can have an impact on the performance of electric showers - this can cause overheating or poor flow due to the pressure being below the minimum requirements. A reduction in water pressure and flow rates can result in temperature fluctuations, inability to achieve a comfortable showering temperature and even cause the shower to not heat at all; this will be especially evident at times of peak water usage.
The incoming water temperature is higher in hot weather. Therefore, if the temperature control isn’t set further towards full cold then the thermal trip will cut in at around 45 degrees to keep the shower at a safe temperature. This will continue to trip while the control is set to too high a temperature. This is not a fault with the shower.
Another problem caused by the higher ground water / mains water temperature is achieving a cool shower. Whenever the shower is switched on the heating element remains on - as the incoming water temperature is currently around 15 - 20 degrees a cool shower may not be achievable. For example if the incoming water temerature is 19°C and the product is a 10.5kW shower with a outlet flow rate at fully cold of 9 litres per minute, then the minimum temperature that is achievable would be 34.8°C.
If these problems persist, check if the water mains stop-cock is fully open. If you have a pressure reducing device and it is set quite low, then try turning this up. Check if your showerhead has limescale blocking the water flow and descale if this is the case.