We were away for a few days and shut off the oil burner/boiler (Weil-McClean Gold) while we were gone. We turned the boiler on when we got home. A day after returning home I heard water running in the cellar - the overflow from the Superstore was discharging into the one gallon pale on the floor and overflowing. The cellar floor was soaked. I flipped the spring loaded pressure release valve at the top of the discharge pipe and the discharge opened up full force. Releasing the valve did not return the flow to a strong trickle instead it was a stronger flow. Finally I turned off the cold water feeding the tank and shut off the boiler. What's going on and how do I correct the problem?