Similar problem here with a SMEG SUK91MFX5 cooker. Decided to take the door off the oven. Instructions are in the SMEG manual so they don't repeating. It's a little fiddly - best done by two people. That's when I realized that the tension on the springs was very different - one was very tight, the other very slack.
Removed door and then carefully placed it handle side down on a solid surface.
To take the door apart, you need to get five screws out. Two long phillips head screws on the inner face towards the top of the door also hold the handle in place. Remove them. Find the Three philps head screws along the base of the door - they are close to the level of the front glass face of the door.
[Note that there are two other screws on the base, and two on the side of the door - these hold the hinge assembly in place. Leave these alone until you're ready.]
With the 5 screws out, lift the inner face of the door off. You willnow see the hinges on either side. Have a look at them.
In our case, one of the two was severely distorted, and the pin holding the spring to the assembly had come adrift. The whole hinge needs replacing as it's not possible to adjust it. The disassembly process took about 15 mins.
I've ordered the part from http://www.smeg-service.co.uk - only about £15 all in.
I hope to report back that it's sorted.
bikesaddle, April 2009