The apartment is shocked by water from the tap and from the shower

Hello! Faced such a problem, in the bathroom the shower is shocking. Sinned on TEN, decided to replace. He removed the boiler, pulled out the heater, but had not yet had time to buy a new one for replacement. When he washed his hands in the kitchen, he accidentally touched the oven with his foot, there was no gas in the apartment, everything was electric. Moreover, when I just touch the oven, it’s normal, but when I turn on the faucet in the kitchen, I put my hand in the water and the other in the oven, it’s beating quite decently. I so assume that perhaps the problem in the soul was not due to the heating element. Perhaps something with the wiring itself? Grounding? Please tell me where to start digging. What could it be?