Hiya,
If he's an electrician and not a Whitegoods engineer then you've firstly go the wrong person in to look at the appliance.
Get a tube of high temp sealant.
Take the door off the appliance.
Take the door apart so you can work on the inner door only.
Take the glass off, clean off all the...
Your repairer is talking rot. Whirlpool have always supplied end user pcbs. Blanks were used by Whirlpool engineers who could write the software to them on site.
I know because I'm ex Whirlpool
You don't need a pcb. Don't know who told you you did but it's 99%certain you don't need it.
4 flashes is a drainage failure.
Get a kettle, fill it and while it's boiling take out the fine filters in your machine.
Once it's boiled, pour it into the sump of the dishwasher getting as much...
You haven't provided the product number or serial number so have to guess at the age.
Continuous flash is a single flash. Single flash is error code F1 which is an NTC fault.
NTC regulates the temperature. It's fitted from the underside, twist fit and has two thin blue wires going to it.
Water hammer is a common fault of the inlet valve.
You've pretty well understood how it should work.
Take the side panel off and watch whats happening.
If you manually activate the pressure switch water should stop, release it and it should take in water again.
Intermittent heating can be a dry joint at the heater relay on the pcb.
However, if there's not enough water, it won't heat.
Water level is controlled by the pressure chamber.
As far as I remember the issue is a lack of water in this machine.
If the transfer pipe is clear then the pressure chamber would be the next item to check.
Its easier if you stick to one thread.
We need the enr number to see what appliance you have.
If you post the enr number and the fd number I'll be able to look up the exact machine you have. That'll maybe help diagnose the fault.