Unplug the appliance.
Take the bulged cover on the rear off.
Take the heater assembly out.
Check the heater to see if it's failed.
If the heater itself is ok, check the thermostats.
One has a coloured dot on it, if it has a small hole on the rear, use a pin to gently reset it.
Reassemble the appliance and try it again.
If no hole, you need to test the thermostat using a multimeter.
If it's open circuit you'll need to replace the thermostats.
Also check the condenser and ducting , ensure they are clean and clear.
Check it out, see what you find.
Hope this helps
Let me know how it goes