1. What is dripping?
1.1 The outlet of the pressure relief valve. Usually copper turned back to a wall with an elbow.
1.2 The condensate pipe. Usually white plastic and should go to a drain, preferably internal.
1.3 A drain cock attached to the boiler feed or return.
2. If 1.1 then check pressure on gauge. If above 3.0 bar, pressure relief valve is letting by. Check:
2.1 That the filling loop is fully closed. If not, close, and let water out (radiator bleed point) until around 1.3.
2.2 The expansion vessel (EV) has air in one half. Remove Schrader valve cap, depress valve. If water comes out (more than a few drops) EV need recharging or possible replacing.
3. If 1.1 and the pressure gauge is normal, get PRV checked and replaced if necessary.
4. If 1.2, water will come out of this while the boiler is running.
5. If 1.3 tighten square shank of valve. If doesn't stop leak, replace washer in drain cock (look for drain cock washers, get type A and type B). Not always easy to do, and wait until system is cold. Otherwise get drain cock replaced.