When I touch the heating cable under water, it is only warm.
It is by all means correct that the JBL ProTemp S heating element only emits what is perceived to be pleasant warmth by the hand. The surrounding water causes the heat to be conducted away very quickly and passed on to the water. Therefore, the heating element is functioning properly. If it is taken out of the water, the glass immediately becomes very hot. The safety shut off is activated immediately. Nevertheless, the resulting heat must escape outside the water after the heating is switched off, which may cause the heater guard to become deformed, as there is no water to cool it. The safety thermoswitch in JBL ProTemp S heaters is by no means intended as an automatic control device which makes it unnecessary to pull the plug before a water change and, instead, is merely an additional safety precaution against accidents involving electricity. Due to its design, the heater may become very hot before the thermoswitch turns it off.