I have a potterton promax combi boiler which seems to be leaking ?

Hi, I have noticed a slight leaking coming from the pressure relief pipe work (located outside the building). I've located the red relief valve and that seems to be closed. I've had to re-pressurise a couple of times now over the last 24 hours. I don't know a great deal about boilers but is there anything I can do myself? Does this mean the pressure relief valve is faulty and will have to be replaced?