Could someone tell me how an electric shower works. I have one in my house and if I use it, even though the water in the tank in cold, the water is still hot. Does the shower actually heat the water itself and how does it do this so quickly?
It takes water from your cold water system and heats it up. There is a heating element inside, which is why the flow is much faster on a cooler than a hotter setting.
The tank you refer to is actually the hot water storage cylinder that's why it is covered with foam/lagging to keep water hot from the boiler/immersion heater.
Water for Electric showers are nearly always fed from the mains cold and the flow/heat of water delivered to the spray is directly proportional to how powerful the rating of the heating element within the shower is HTH Tez