A leaking bathroom faucet is fixed by shutting off the water, replacing the worn cartridge, washer, or O-ring, and testing the faucet.
A dripping bathroom faucet looks like a plumbing project, but it usually comes down to a parts swap. The drip, seep, or weak stream traces to one small internal component — usually a washer, O-ring, cartridge, seat, or spring — that has worn out. With a matching replacement part and basic hand tools, most homeowners finish the repair in about an hour. The repair order never changes: water off, part out, part in, test.
Start With the Water Off and the Faucet Drained
No repair starts until the water is off. Turn the supply valve under the sink for the side you are working on — hot or cold — clockwise until it stops. If a valve is stuck or missing, shut off the home’s main supply instead.
Open the faucet fully after the water is off. That relieves pressure in the line and drains the remaining water, so nothing sprays out when the first fitting loosens.
Moen’s cartridge-replacement guidance lists a Phillips screwdriver, hex/Allen wrench, adjustable pliers, needle-nose pliers, and safety glasses as the basics for this job. Keep a small container and an old towel under the valve to catch leftover water.
Faucet Repair by Symptom: Which Part Is Worn?
Where the water escapes points to the part causing the leak. Match the symptom in the table below to know which piece to order before the handle comes off.
| Faucet Symptom | Usual Culprit | Part to Replace |
|---|---|---|
| Drips from the spout with the handle closed | Worn washer, seat, or cartridge | Washer and seat first; replace the cartridge if the drip stays |
| Moisture around the handle base | Worn O-rings or seal | O-rings, then reseat the handle |
| Two-handle faucet leaks around the valve stem | Worn seat and spring, sometimes the stem | Seat and spring; inspect the stem |
| Weak stream or irregular spray | Clogged aerator or mineral buildup | Remove the aerator, clean it, and flush the lines |
| Drip continues after a cartridge change | Wrong cartridge, or seat and spring still worn | Confirm the model number, realign the cartridge, inspect remaining parts |
Faucet parts are model-specific, and a mismatched cartridge, seat, or O-ring can turn a slow drip into a worse leak.
- On a Moen faucet, the model number is usually on the UPC label of the original box or on the instruction sheet. If both are gone, Moen’s product finder and Identify My Product tools can fill in the gap.
- If the part still cannot be identified, Moen’s customer service can help, and a plumber is the fallback for older faucets with corroded valves.
If you need several parts at once, our tested bathroom faucet repair kit picks show which kits bundle the washers, O-rings, seats, and springs most repairs need.
Reassembly, Flushing, and the Final Leak Test
Put the faucet back together in reverse order, then turn the water back on and watch. Repairs typically fail at this point when a part was misaligned or a nut was overtightened.
- Insert the new cartridge or stem straight into the valve body. Align it with the slot or notch designed for it, hold it seated, and tighten the retaining nut only until snug — cranking it down can crack the housing.
- Reinstall the handle and trim in reverse order. On a two-handle faucet, replace the seat and spring before reassembly if the drip pointed there.
- Take the aerator off before opening the water. Then open the supply valve slowly and run hot and cold briefly to push sediment out. A blocked aerator is the reason many repairs still look like low pressure afterward.
- With full flow restored, check the stem, base, and supply connections for drips. Close the handle, wipe everything dry, and wait a few minutes. Done means no drip and no moisture.
If the dripping faucet is a Moen single-handle model, the cartridge swap is the standard fix and follows Moen’s cartridge-replacement guidance — including the main-water shutoff and the final test under the basin.
FAQs
Do I Need a Plumber to Fix a Faucet That Drips?
Usually not. A drip is typically traced to a worn washer, cartridge, O-ring, seat, or spring, and swapping that part takes hand tools plus about an hour. Call a plumber when the supply valves will not shut off, the valve body is corroded, or no replacement part can be matched to your faucet.
Why Does a Bathroom Faucet Drip After a Cartridge Replacement?
The usual reasons are a cartridge that does not match the faucet model, a cartridge seated crookedly before the retaining nut was tightened, or a worn seat and spring that were left in place. Confirm the model number, realign the cartridge, and inspect the remaining parts before ordering anything new.
Where Is the Model Number on a Moen Faucet?
Moen usually prints the model number on the UPC label of the original box and on the instruction sheet. If neither is available, use the product finder or Identify My Product tools on the Moen parts page, or call Moen customer service Monday through Friday, 8 a.m. to 7 p.m. Eastern.
References & Sources
- Moen. “Cartridge Replacement Guidance.” Official cartridge swap steps, tool list, and safety notes.
- Moen. “Replacement Parts.” Official parts lookup and model identification tools.
- Moen. “Customer Support.” Phone 1-800-BUY-MOEN, Monday–Friday, 8 a.m. to 7 p.m. ET.
