This heater circuit is designed using common electronic components .
When S1 is activated C1 is discharged by S1, causing voltage on C2 to grow slowly.
Considering the ratio C1: C2, C2 capacitor is fully charged after about ten shareholders of S1. IC1b integrated circuit is connected as a Schmitt trigger which presents an important hysteresis. After S1 was down seven times, IC1b relay feed via T1's. Then, the capacitor C2 is discharged slowly through R5. After a short time (1 to 2 minutes, adjustable P1), its output voltage drops to a level IC1a the heating element is interrupted.