Dishwasher stopped heating. PCB is fine with no signs of damage. Is there a resettable thermostat or is it a bung water heater?

E3 - Water heating time out or fault

The dishwasher has failed to heat with water in a reasonable time or has failed to detect the water heating element.

Check water heating element wiring
Check water heating element
Check wiring to main control module

Dado

HEATING (ELEMENT) ERROR // Water heating error
The manufacturer has assigned this error or fault code to indicate a problem with the water heating circuit. Turn off the circuit breaker to the dishwasher for 30 minutes, allowing time for the appliance to cool; then restart the cycle. If error returns, check the heating element for continuity and check the wiring harness for any obvious signs of damage. If the heating element shows infinite resistance after testing with an Ohm meter, replace it.

It's usually behind the control panel you have to remove the screws on the door

Your thoughts on pcb are most likely correct

measure the heating element resistance it should be around 25 ohm.
otherwise it is the problem.

You can replace the relay, sometimes it stop working with no external damage signs

The dishwasher will heat the water to a temp of aprox 140deg if the heater is not working then the dishwasher will not shut off because it has to heat the water to a point where a thermostat will close during the heating time the dishwasher time stops advancing, also heater is used to heat the air for dry cycle

F3 error fault code
The heating cycle is not working. The error is indicated after several electronic checks are done over a 25 minute period. Therefore if the heater heats too slowly or the heater is open circuit or indeed the electronic control PCB is defective, each of these will indicate F3. The twist is, if the NTC is fluctuating in its reading it also can indicate F3 and not F1.

the heater is in ther base of the appliance usually accessible by taking side panel off. not all heaters of this type have a resettable stat