Guys, if your beers carb fine, and are good for a few weeks, then they become gushers, then you have an infection.
Normally, once a beer reaches it's carb level, (which is when the yeast has eaten all the sugars you add at bottling time.) and is stabilized, it can't carb any further, UNLESS something is breaking down the unfermentable sugars, and eating them.
And that means a bug of some sort.
You need to look down the chain, like in your bottling process, for something you're missing in regards to sanitization.
Take a look for example at your spigot, hop matter an other gunk can often get lodged inside, and cause you problems. There's a pic of one broken apart to show the gunk lodged deep inside. But I can't find.
I've opened beers of mine that were carbed 5 years ago and they didn't gush. Unless there's a problem, in terms of carbonation, beers reach their level of co2, and stabilize, they don't then start gushing unless something's wrong.