Nice try mate but you still wont get any diy advice to work on your boiler. It sounds like an easy fault to remedy. Get your wallet out and pay a professional to repair it.
"in all honesty i Wasn't convinced he knew what he was doing", yet you think your father the "diyer" is competant to open up a positive pressure boiler and tape up the electrode.. call in a gas safe registered engineer.
Sounds more like the pressure guage is goosed m8..the prv will open ip if its over pressurised and if the guage isn't working then it will be over pressurised.
The boiler is positive pressure it should be tested around the seal with a match to check for leaks, if the match blows out then the case or seal needs adjusting. Get him back to test it.these boilers are death-traps if not serviced correctly. Do younhave a carbon monoxide detector?,if not get...
The diaphragm inside the valve creates the seal. Order the service kit easy job,drain the ch system,open the valve,replace diaphragm and front seal,add inhibitor to system,fill up and bobs your uncle etc etc.