the dripping from the prv (pressure relief valve) is due to a faulty or dirty valve, it is worth isolating boiler from heating circuit (via the isolaters on the flow and return) and releasing the pressure from the boiler by turning the red knob on top of the prv until the gauge reads zero and then removing the prv from the boiler and undoing it to get to the seating washer, this can be cleaned and greased with a little petrolium jelly and refitted (or replaced whilst your at it ! ) once you have re opened the flow and return and re pressurised the boiler via the filling loop to 1.5 bar the overflow outside should cease..... this is the most common solution to this problem however if even after replacing the prv it still discharges through the outlet then this could point to a depleted/faulty expansion vessel and i wont even go into this as this will require a bit more in depth engineering ability but the first method i suggested should do it and save you a replacement boiler !
mark the gay boiler man, November 2008
