Did you shut off both hot and cold angle stops under the vanity, then open the old faucet to confirm no flow?

Measure (or look up) the hole configuration on your sink. Does it match the new faucet?

Common bathroom configs: single-hole, 4" centerset (3 holes, 4" center-to-center on the outer handles), 8" widespread (3 holes, 6–16" apart).

Look at the sink around the mounting holes. Any cracks, chips, or hairline fractures in the porcelain / china?

Bathroom sinks are thin and brittle. A pre-existing crack will spread when you torque mounting nuts.

Are you also replacing the pop-up drain assembly (lift rod, linkage, and tailpiece), and what is the existing tailpiece made of?

Most new faucets come with a new pop-up assembly. The existing tailpiece threads into the sink from below; cast iron / brass tailpieces in old sinks can seize.

What do the supply lines look like between the angle stops and the old faucet?

Do you have basin wrench, channel locks, plumber's putty (or the silicone gasket the faucet supplies), PTFE tape, new braided supply lines, towels, and a small bucket?

plumbing troubleshooting

Replace bathroom faucet

Common symptoms: replace bathroom faucet; install lavatory faucet; bathroom faucet swap; pop-up drain replacement; vanity faucet

Stop and call a pro if:

pop-up drain linkage may be brittle
thin sink material can crack under wrench torque

Step-by-step diagnostic flow

Step 1
Did you shut off both hot and cold angle stops under the vanity, then open the old faucet to confirm no flow?
Step 2
Measure (or look up) the hole configuration on your sink. Does it match the new faucet?
Common bathroom configs: single-hole, 4" centerset (3 holes, 4" center-to-center on the outer handles), 8" widespread (3 holes, 6–16" apart).
Step 3
Look at the sink around the mounting holes. Any cracks, chips, or hairline fractures in the porcelain / china?
Bathroom sinks are thin and brittle. A pre-existing crack will spread when you torque mounting nuts.
Step 4
Are you also replacing the pop-up drain assembly (lift rod, linkage, and tailpiece), and what is the existing tailpiece made of?
Most new faucets come with a new pop-up assembly. The existing tailpiece threads into the sink from below; cast iron / brass tailpieces in old sinks can seize.
Step 5
What do the supply lines look like between the angle stops and the old faucet?
Step 6
Do you have basin wrench, channel locks, plumber's putty (or the silicone gasket the faucet supplies), PTFE tape, new braided supply lines, towels, and a small bucket?

Possible outcomes

You're ready — proceed with the swap

high confidence

Water is controlled, hole pattern matches, the sink is sound, the drain and supplies are workable.

Safe next steps

Disconnect the supplies at the faucet shanks, then unhook the lift-rod linkage from the pop-up clevis
Unscrew the slip nut on the tailpiece (P-trap connection) and the locknut holding the pop-up flange; lift the old faucet out
Clean the deck, set the new faucet (silicone gasket or a thin bead of plumber's putty if specified), and tighten mounting nuts evenly
Install the new pop-up: putty under the flange, locknut and washer from below, thread in the pivot rod, hook to the clevis with the lift rod
Connect new braided supplies, hand-tight plus a quarter turn
Open the angle stops slowly, run hot and cold, fill and drain the basin to check the pop-up seal and the P-trap joint

Stop — fix the angle stops first

high confidence

A shutoff that won't close means you can't safely disconnect the supply.

Safe next steps

Run the angle-stop-replacement workflow, or shut off the house main and replace the stops now

Angle stop won't fully shut off

Pause — buy a deck plate / escutcheon

high confidence

Exposed holes look bad and let water and toothpaste drip into the vanity.

Safe next steps

Order the matching escutcheon from the faucet maker, or buy hole covers in the same finish

Stop — faucet doesn't fit this sink

high confidence

A widespread faucet won't reach across a centerset sink, and a single-hole faucet won't cover a 3-hole sink without a deck plate.

Safe next steps

Exchange the faucet for one that matches your sink's hole spacing

Hole spacing mismatch between sink and new faucet

Stop — cracked sink risk

high confidence

Tightening mounting nuts on a cracked porcelain sink usually finishes the crack and turns a $200 faucet job into a $400+ sink replacement.

Safe next steps

Photograph the cracks for reference
Decide whether to replace the sink now (often the right call) or have a pro evaluate the crack

Pre-existing cracks around faucet mounting holes

Stop — call a pro for the seized drain

medium confidence

An old painted or seized tailpiece can crack the sink when you force it. This is a common pro service call.

Safe next steps

Photograph the underside of the sink and the tailpiece
Leave it in place for the plumber

What to document for a pro

Photo of pop-up assembly and tailpiece
Sink material (china, cast iron, stone)

Old pop-up drain assembly is seized in the sink

Stop — legacy supply line

medium confidence

Lead or unknown legacy metal supplies should be assessed by a pro before being disturbed.

Safe next steps

Photograph the supply line and angle stop
Leave the existing connections alone until evaluated

What to document for a pro

Photo of supply line and angle stop
House age if known

Lead-soldered or unidentified legacy supply line

Pause — gather tools first

high confidence

You don't want to be elbow-deep in the vanity realizing you're missing a basin wrench.

Safe next steps

Buy: basin wrench, PTFE tape, new braided 3/8" comp × 1/2" FIP supply lines, plumber's putty
Stage towels, a small bucket, and a headlamp

Diagnostic guidance only. If unsure, stop and call a licensed professional — gas, electrical, and refrigerant work is hazardous to untrained users.

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