The gaps are a bit big for sand. Perhaps the only problem is a one time settling or perhaps it is heave from frost, how cold does it get where you are? I don't suppose you know what the stones are laid on, is there a specification supplied by the installer? How long ago was the job done?

Thanks "inkognito" for the follow up (and I apologize that I didn't respond earlier; newby error: I thought I'd receive an email notification if anyone posted. Oops.)

To answer your questions:
We get down to about minus-5 Fahrenheit (-20 C).
Unfortunately I don't know what the stones are laid on, nor who the installer was--or even when installed.

I just hate the thought of having to pull everything up and relay the stone unless necessary. (What I'd love to do is pressure steam clean them... and as little else as possible. But, is that realistic?

Thanks!