When is a flat not a flat?

Got up Tuesday morning, wheeled the bike out of the garage and heard an odd squeaking sound . Looked down and sure enough the rear tyre was flat. Didn't notice it on the ride home the night before so assumed it was a really slow one and had deflated over night.

So reinflated but didn't risk the ride to work, just in case. Came home expecting the tyre to have deflated only to find that it had stayed up. Left it over night, just in case it was reeeeaaaaallly slow and...nothing. Pressure was as I had done it on Tuesday morning - normal - 36psi

Now I am totally confused. Unless I have p***taking vermin who can undo the dust cap and stick a stick in the valve then redo the dust cap in the garage I don't know how it went flat.

Its due for its service and MOT this month will get it checked then but any of you got any other ideas.

i had this on my curvy....... comming from bradford to cardiff i thought i got a puncture, so i came off at birmingham to get it sorted, but i could not find anywhere, by now it was flat as a pancke, anywho, i pumped it up and continued home, it never went down again.

i put it down to a dodgy valve?

Thanks for that Hovis.

I'll get 'em to check out any way when it goes in for its service etc. Just to be sure, to be sure.

Thanks again.

Had a dodgy valve, as Hovis said, last year. It would drop the pressure down to 28psi everytime but it wouldn't get any lower, guessing that was the pressure limit of the knackered valve (if that can happen?).

Got it replaced and no problems since....