I'm assuming that the place where it was leaking was the T&P valve?
That is designed to release under any one of two conditions: excessive pressure, or excessive temperature. Weeping a little is likely if the expansion tank is shot (or there's none installed). But, a strong flow is not normal. What was the temperature of the water being discharged?
If I had to guess, I'd guess that your expansion tank is shot and the T&P valve has some mineral deposits on it, and once it tripped, it wouldn't reseat. So, I'd check the expansion tank, and then replace the T&P valve unless the boiler was running away, and the tank was excessively hot.
It's possible, if you have excessively high water pressure, that your PRV is shot. You should also check the incoming water pressure to rule that out.