[Jabberwocky]

While all possibilities regarding this has been compiled above, you should also get the rim itself checked. It's highly improbable, but the rim itself may have a bend or crack somewhere leading to the loss of air pressure. This is probably not the case, but do get it checked just to rule it out.

The best way to resolve the issue is to get it sorted with a reputed tire shop, not just a puncture shop. A tire shop will have the space and expertise to sort it out quickly and thoroughly.

Either way good luck with the troubleshooting.

[adrian]

The factor of wheel heating up due to bad bearing or dragging brakes should be ruled out. Tyres heating up tend to loose tyre pressure gradually.