Heater turns off the 3d printer?

I have Velman Vertex K-8400 and the following issue:

when I am heating up the nozzle, I have a weird interruption, it looks like the power supply is turned off and on, but the heat goes up… Those interruptions are well seen when I’m trying to move the axis (motor) in different directions. On the other hand, when the heater is turned off I can freely move motors.

Any thoughts?