Signs of wear of the fireclay floor after a short running time are very surprising and not normal. There are some important points to take care of the furnace, please be sure to follow them:
Never use moisture, water, detergents or even wet rags for cleaning. This can cause thermal shock. Then the material contracts much too quickly and cracks may appear!
It is sufficient to remove the ash and embers with a brass broom.
Change the fire weekly in order to stress the fireclay floor equally.
After work or in the evening, close the door to reduce the heat or temperature in the oven very slowly.
Under the floor should be at least 20 cm thick insulation to retain heat and ensure slow cooling.