Prier silcock turns on by itself

I have 2 Prier 180 freezeproof silcocks that turn on by themselves, almost to full flow. I have tried to turn them off very tightly, however it happened twice to one of them.

Before I replace them or even try a repair, has there been any suggestions to this problem?

Thanks..

Have you checked the pressure of the incoming water? too much pressure and a loose packing nut could cause that.

It's city water pressure that has been the same for years. Did not have this problem until we installed these new faucets. Could be a loose packing nut though. I will check this.

hose faucets.

Some of them had a "quick opening" stem, and since it had a very steep pitch, and a non adjustable packing "O" ring, pressure could open them. They fairly quickly reverted to the old thread, but you probably have one of the old ones. The nonfrostproof ones were easily fixed by replacing the stem unit, I don't know if you can do that with the frostproof ones.