Hi, I has this cylinder fitted a year ago in a flat with economy 7 heating on the tank. The tenant phoned me up today and it appears water has been coming out of the pressure relief valve, and as a result where it drains into 1 1.5 waste pipe, this has warped due to the heat of the discharge water. The water coming out of the taps is vey hot. Any idea please what could cause the water to come out of the pressure relief valve? Thanks