How a single-handle faucet works and fails
A single-handle faucet mixes hot and cold water inside a cartridge or a ball valve. Moving the handle slides or rotates parts inside, and rubber seals keep water from passing where it should not. When those seals wear or mineral scale builds up, the faucet drips from the spout or leaks around the base.
Brands such as Moen, Delta, Kohler and others each use their own cartridge, so identifying the faucet is the first step in a successful repair.
Before you start
Close the stop valves under the sink, turning them clockwise. If they will not turn, close the main shutoff. Open the faucet to drain the lines and plug the drain so small parts do not fall in.
Take a photo at each step so you can reassemble in order. Keep parts in a tray in the order they came off.
Taking the faucet apart
Pry off the cap on the handle, remove the screw beneath it and lift the handle off. Unscrew the retaining nut or clip, then pull the cartridge straight out. A cartridge puller helps if it is stuck with scale.
Inspect the o-rings and seats for cuts, flattening and mineral crust. Bring the cartridge to a plumbing supplier to match the replacement exactly.
Local note: water in Marblehead and your faucet
Marblehead buys all of its water from the MWRA, and the town tests lead and copper at 15 homes a year. Its 2021 letter reports a 90th-percentile lead result of 1.67 parts per billion, well below the action level. The letter does not give a hardness figure, so test your tap or ask the Water and Sewer Department if scale is a concern.
If your faucet clogs with white deposits quickly, scale is a likely cause, and a vinegar soak for the aerator often helps. Metal and mineral buildup can show up at the aerator first.
Use the maker's guidelines for your model, which list the matching cartridge number and the torque for the retaining nut.
Faucet still dripping?
Call the 24/7 line and a plumber will fix or replace it.
Installing the new cartridge
Coat the o-rings with plumber's grease and push the new cartridge in, lined up with the notch or tab. Replace the retaining clip or nut, reattach the handle and turn the water on slowly. Check the spout and the base for drips.
If the faucet still drips from the spout, the valve seat may be pitted. A plumber can reface it or replace the faucet.
When to replace instead of repair
Pitted or corroded body
The faucet may leak around new parts.
Discontinued cartridge
No match is available.
Leaks under the sink
A cracked base or supply line is a replacement.
Low flow despite cleaning
The inlet ports may be blocked with scale.
Check the stop valves while you are there
Old stop valves under the sink often seize or weep when turned. If one drips, replace it before you reassemble. See faucet repair for the full service and plumbing installation if you want a new fixture installed.
Tools and parts to have ready
Most repairs need an adjustable wrench, a hex key set, a screwdriver, pliers, plumber's grease, a flashlight and a small tray for parts. A cartridge puller is helpful for stubborn cartridges, and a rag protects the finish from tool marks.
Buy the cartridge and o-rings before you start if you can identify the brand. If not, take the old cartridge to the supplier. A close match that is not exact will leak.
Kitchen pull-down faucets and other variations
Kitchen faucets with pull-down sprayers have a hose and a weight under the sink that you disconnect first. The cartridge sits under the handle, as in a bath faucet, but the spout may rotate on o-rings that also wear.
If the spout leaks at its base, replace the spout o-rings. If the handle is loose, the set screw or adapter has backed off and needs tightening.
Testing and finishing the repair
Open the faucet slowly with the aerator removed to flush out any debris that loosened during the repair. Watch the base and the spout for several minutes with a dry paper towel nearby. A faucet that holds dry for ten minutes is done.
Reinstall the aerator, wipe the finish with a soft cloth and note the date and the cartridge model in your home records. The next repair will be quicker, and a plumber can see what was fitted.
If you are unsure at any point, stop and call. A stripped screw, a cracked body or a stuck cartridge that will not budge is where a small repair becomes a big one, and a plumber has the pullers and the parts to finish the job cleanly.
Single handle faucet questions
A worn cartridge or seat lets water pass the closed position. Replace the cartridge first.
The o-rings around the cartridge or body have worn. Replace them when you replace the cartridge.
Only if the stop valves under the sink will not close.
Bring the old one to a plumbing supplier or look up the brand and model.
Most take under an hour once you have the correct part.
Yes. The crew serves Lynn and Swampscott as well.
Mineral scale may be holding it. Soak with vinegar and ease it off with a puller rather than prying.
If parts are not available, replacement costs less than repeated fixes.