Hi

My question I guess is for a plumber who knows about electric water heaters and tanks.

To get hot water out of my kitchen tap I have to turn the tap fully on, if I turn it back to half way it will soon become luke warm/cold. I have an electric water heater and the pipe that the hot water comes through from the tank gets very hot immediately you turn the tap on, much hotter than what actually comes out the tap when the tap is on full. The pipe from the water heater remains very hot even as the kitchen tap has started to run cold.

Is this a single handle faucet or one with knobs?

Unless this same thing occurs at other faucets this is not a water heater problem.

Most likely the problem is caused by debris trapped in the hot water side.

Turn off the cold water stop valve under the sink. See what kind of flow and pressure you have on the hot water side. Most likely the flow will be quite small.

The debris can be in the faucet or it can be in the hot stop valve. If you have flexible supply tubes switch the hot to the cold and the cold to the hot. Open the faucet. If the hot side is still restricted the blockage is in the faucet. If you get full flow out the hot side (the water will be cold) the restriction is in the hot water stop valve. This an easy thing to do if you have flexible supply tubes.

Not so easy if you have hard supply lines. Dissemble the faucet, hold a cup over the open faucet, turn the hot water on and blow out the hot side of the faucet.