Heating and temperature

Yarnfan

We have a Truma electric heating with a dial on the wall of the motorhome. We set it to say 7 out of 10 on the dial then during the day it can reach 18 degrees C but when I was cold one night the temperature of the motorhome had slipped to 14 degrees C in
the night.  Does the dial on the wall set the output of the electric heater or is there a thermostat and if so why the change in temperature?