The drive belt on my washing machine - a Hotpoint Aquarius WMA33 - came off and I’m having problems refitting it. Whatever I do, it rides up over the inner rim of the wheel on the back of the washing drum. I’ve tried adjusting the position of the belt on the motor without success.
Picture of drive belt on motor here.
Picture of drive belt on wheel here.
Hopefully I’m missing something obvious.
And yes, I have paid the red sacrifice. 
Can you adjust belt tension? It might be too tight. You should be able to press the belt with your finger and it should offer firm – but not rigid – resistance. You should easily be able to depress the belt 1/4" or more before it offers strong/final resistance. Making belts very, very tight tends to see them “walking”.
Obviously, all other positional adjustments available should be checked to ensure the drum and motor wheel are lined up, too.
I’m not sure but I think that is the case.
Could this be due to the age of the belt? It’s at least 7 years old and probably 10.
Where do I find those adjustments?
Well, the belt needs to be replaced first. Until you eliminate THAT variable, ALL bets are off.
Well, the issue is now moot. It turns out that the bearings have gone and the cost of all the various spare parts is almost as much as a new machine. So I’ve bought one.
I see the question is moot, but for purposes of archival knowlege:
Most vee belts will function to some degree up to the point where they break. They can get hard and slip, or lose chunks and get noisy, but for the most part they will still mostly “work”.
If a sound belt doesn’t stay on, that is a symptom, not the disease. The pulleys have to be aligned and unbroken, and need to turn without binding. Failed bearings would cause binding or misalignment, so that is why the belt wouldn’t stay on.
