Match the faucet to your sink's hole layout, shut off both stop valves, and remove the old faucet. Mount the new one on its gasket or putty, assemble the pop-up drain, connect hot and cold supply lines, then flush the lines and clean the aerator. Check every joint for leaks.
Step 1: Does the new faucet fit your sink?
Look at the top of the sink or counter before you buy. The count and spacing of holes decide which faucet works.
Moen's centerset sheet, for example, says the faucet "Fits 4" centers and through a 1" minimum diameter hole." Its widespread sheet shows 8 to 16 inch centers. A single-hole faucet needs one hole. A faucet that is wider than the holes you have will not mount, and adding holes in a porcelain or stone top is a job for a fabricator, not a drill.
Also check that the faucet comes with a drain. Moen's instruction sheets mark the water supply lines as not furnished, so plan to buy two supply lines sized for your stop valves.
Step 2: Shut off the water and empty the lines
Close both stop valves under the sink, hot and cold, by turning them clockwise. Open the old faucet to release pressure and drain what is left. Moen's cautions say to open the faucet handles to relieve pressure and confirm the shut-off is complete.
If a stop valve will not close or drips when you turn it, stop. Close the main valve instead and read what to do when an angle stop will not shut off completely before you go on.
Step 3: Remove the old faucet
Put a bucket and a flashlight under the sink. Disconnect the supply lines from the faucet, then loosen the mounting nuts that hold the faucet to the deck. A basin wrench reaches nuts you cannot get a regular wrench on. Disconnect the pop-up linkage at the drain, lift the faucet out, and clean the deck so the new gasket sits on a flat surface.
Step 4: Mount the new faucet
Follow your model's sheet. For Moen's centerset, the instructions say to be sure the lavatory or mounting surface is clean and dry, set a bead of plumber's putty around the inside lip of the gasket, position the gasket on the deck, assemble the clamp bars (with spacers on thinner bowls or counters) and mounting nuts onto the studs, and set the faucet's supplies and studs down through the deck.
Here's the catch. The same sheet warns you to "Hold the faucet connection nipples with a wrench when tightening to prevent twisting and collapse of the tubing." Wrench the nipple, not the tubing, and the tubing survives.
Widespread faucets work in three pieces: a spout and two valve bodies. Moen's widespread sheet has you set the valve bodies so their tops sit 3/8" to 7/16" above the deck, make the final tightening with a basin wrench, and hold the valve bodies still with a second wrench on their flats.
Step 5: Build the pop-up drain
Most bathroom faucets include the drain assembly, and this is where leaks hide. Moen's sequence is to put a 1/4 inch bead of plumber's putty under the drain seat, apply pipe joint compound or thread seal tape to the top threads of the drain body, push the body up through the sink opening and screw the seat on, and point the pivot rod opening toward the back. Tighten the mounting nut until the drain body is snug, and wipe off the squeezed-out putty. Then connect the lift rod, the strap and the spring clip, and adjust the rod so the stopper opens fully.
If the stopper never seals later, adjusting a sink pop-up stopper walks through the linkage.
Step 6: Connect the supply lines
Connect hot to hot and cold to cold, using the markings on the faucet and the stop valves. Then follow the supply line maker's tightening directions exactly, since some lines are designed to be tightened by hand only. Replacing a toilet supply line uses the same connection, if you want a second look at the technique.
Step 7: Flush the lines and clean the aerator
This is the step many guides skip. Moen's sheet says pipe chips, sand, stones and other solids "can damage the sealing surfaces of the cartridge and cause a leak," and tells you not to operate the valve until you have followed its flushing instructions.
For the centerset: turn the valve to full cold and run the cold supply for 15 seconds, then turn to full hot for 15 seconds without closing the valve. Close the valve, unscrew the aerator, clean the cone screen, replace the aerator and check for leaks.
In Phoenix this matters more than usual. Phoenix water is hard, and mineral flakes dislodged from old pipes and stop valves can end up in a new cartridge or aerator, so do not skip the screen cleaning.
Step 8: Check for leaks, then check the flow
Run the water at full flow, then watch each connection with a dry paper towel. Check the drain by filling the basin, then releasing the stopper. Look again in an hour and the next morning.
Flow is regulated here. Phoenix's amendments to the 2024 plumbing code set private lavatory faucets at a maximum of 1.5 gallons per minute at 60 psi, in place of the model code's 2.2 (the residential code amendment says the same for lavatory faucets). EPA notes that WaterSense labeled bathroom faucets use "a maximum of 1.5 gallons per minute," so a WaterSense model satisfies the code. For more on that trade-off, see whether low-flow faucets work well.
When should you call a plumber?
Call for help when:
- a stop valve will not close, or leaks from its stem
- the faucet needs a new hole drilled in a stone or porcelain top
- you are moving the faucet or the supply lines, which is a plumbing alteration with its own permit rules
- the drain connection leaks after you have redone the putty and tightened nuts properly
If you are replacing a kitchen faucet instead, use the kitchen faucet steps. For a wall-mounted spout, read wall-mounted bathroom faucets. For a standing leak or valve problem under the sink, HQ Plumbing and Air is licensed and insured, offers 24/7 emergency service and gives free estimates with the price up front.