It sounds like someone made a firm stroke of the pump against a presta valve that momentarily refused to open, stretching the coiled tube that actuates the geared needle as the pressure spiked over ~200psi.
I've fixed these by manually twisting the needle backward. Note that forcing the needle has a ratchet effect in one direction, and may skip a tooth in the gear mech. This will create a gross readjustment to the needle's rest position, necessitating some follow-up twisting/bending of the needle to a finite pressure/position verified by a guage (i.e., the gears will slip under force in only one direction). It's not usually accurate to zero the guage, since zero usually has the needle pre-loaded in the negative direction against a stop pin.
If you can twist the needle on the shaft or remove the needle and push it back on in a more proper position, it may be easiest/best. You'll also have to lift/bend the needle a bit to go backward past the stop pin and then back again after resetting. In most cases, the final tweak toward calibrated accuracy is easiest to achieve by bending the needle itself. Note that a full turn or so may be needed to reset the needle back even a few degrees, but this seems to cause no harm.
I have re-set many geared, bourdon-tube guages this way, and none was the worse for it. The important thing though is to have a usable standard (guage) for establishing reasonable accuracy.
David Snyder
Auburn, CA usa
> The pressure gauge on my Silca Superpista floor pump has suddenly gone all
> wonky on me -- reads 40psi when at rest.
>
> Anyone had this problem and can suggest a quick fix?
>
> Thanks
>
> Emanuel Lowi