Astro LT -88 Heater fan problem

The heater fan will not stop if it´s in pos. 1-3, even after i turned of the engineen. Twice i´ve forgotten to turn of the heater fan and after one night the battery will be empty. Could the problem be a relay or resistor?
I´ve tried too find this out here in sweden but with no luck, I hope someone out here can help me.