When a dishwasher door suddenly becomes very heavy and 'falls' open it is generally due to one of two problems or a combination of both. These problems are,
A) broken springs
B) broken pulley cords (which are attached to the springs)
If you are half handy with a screwdriver then both of these problems can be overcome by googling the process plus purchasing the parts from E-spares for the springs (£11) and Partmaster for the pulley cords (again £11) plus postage.
No doubt you'll land up with a couple of screws left over, but it beats the hell out of paying £100 to some Repair Chap.
NB: if you have a HJA8630 only take the side panels off the machine to gain access to what needs to be done. No need to take integrated front door off machine!!!!,,,
NB2: learn from my typical and mistaken blokes approach (no need for instructions - I'm a bloke and I can do this) by watching the instructional videos available on You Tube
You no doubt will derive great satisfaction from doing it yourself and then being able to spend the money saved on red wine!
Steve D, August 2015