Can you post the model number of the appliance please?
do you need anything else?
Sorry for the delay, had to dig out the service manual.
If you've replaced the heater, and the heater/thermostats are ok, I'm afraid the cause of the problem is going to be the main control board.
The heater relay isn't switching or has burned out, so no power is getting to the heater.
Sorry, looks like you need to check the thermostats again (test with damp laundry in the machine when you test it for drying) and the heater.
If you confirm they are good and no power to them, it's the board.
Hope this helps
Let me know if you need more help on this.