A tap that drips is usually the washer in the head
I lay awake in March listening to the bathroom tap. A drip every few seconds into a stain on the enamel. I thought the tap was finished. In the morning I isolated it at the valve under the basin, opened the tap to drain what was in the spout, and took the head off. The washer was a brown disc with a bite out of one side. I put a new one in, the same size, and the drip stopped. The tap was a tap. The washer had packed up.
On an old pillar or bib tap the head holds a jumper and a washer. When you close the handle, that washer sits on the seat and shuts the water off. If the washer is hard, split, or missing a chunk, water still passes. You hear it at night. People replace the tap. The body was fine.
I isolate first. Valve on the supply if there is one. If I cannot isolate that tap, I stop. I do not start on a live pipe. I do not re-pipe a bathroom for a drip. Head off, washer, back on. If the seat is scored and I cannot face it, I stop again. A new washer on a grooved seat will drip by Friday.
Hose fittings leak at the washer, not the hose is the same cheap disc on an outdoor tap. A water butt that stains the path is usually the tap is the barrel in the garden. A tap adapter that does not match the thread is why an outdoor fitting weeps even after you change a washer. Indoors, match the washer to the jumper you actually have. Almost the right size is a drip you made.
When I check I look at the old washer before I bin it. Size, thickness, the hole in the middle. I take it with me if I am unsure. I also look at the seat in the body, a light down the spout or a finger if I can reach. A ridge you can feel is scored. I will not invent a re-seat tool I do not own. If I cannot face it, the job is bigger than a washer and I leave it.
I put the head back square and do not crank it until the chrome rings. Tight enough to seal the body washer under the head, not so tight I strip the thread. I open the isolation, then the tap, and I watch. A drip from the spout is still the seat or the washer. A weep from under the head is the fibre or rubber ring on the headgear, a different disc, still not a new tap.
Skip taking the head off with the water on. Skip a washer from a mixed tin that only looks close. Skip PTFE on the washer face. The washer has to sit, not skate on tape. Skip a ceramic-cartridge mixer if you do not have the part and the isolate is unclear. That is a different tap. I am writing about a head with a washer. Skip calling a plumber for a disc you can see, and skip becoming one for a seat you cannot face.
Night is when you notice. Winter, heating on, the house is quiet enough to hear it. A dripping hot tap also wastes heat you already paid to make. I still only change the washer. I do not chase the heat source.
I do not need a new basin because the tap dripped. I need the supply isolated, a washer that matches, and a stop if the seat is gone.
If I later add a buy link here, it will be a paid promo.