TSR24ACW stopped working but fan kicked in?

My heater has been working recently until the other morning no heat felt from it. I've just changed the fuse for another on the switch on the wall and as I turned up the output from 1 to 3+ the fan at the bottom of the heater has kicked in and heat is coming out. How can this be if the heater itself had not heated over night? Very confused!
Put the original fuse from the switch on wall into another appliance and that works.

Any assistance to what the problem might be to why the heater in the main has not heated would be very useful