Step 1: Make sure you have new parts available
You can fix most problems with the replacement parts available at hardware stores and home centers. A plumbing parts distributor will carry a much larger selection and may be able to special-order hard-to-find items (look under “ Plumbing Parts and Supplies” in your local Yellow Pages or online). There are thousands of different faucet replacement parts available, so bring your old parts to the store for a proper match. If your valve is highly corroded or the finish is wearing off, replace the entire faucet.
Step 2: Disassemble the faucet
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Photo 1: Pry off the handle insert
Shut off the water supply to the faucet and open the valves to drain excess water from the system. Pry off the handle insert with the thin blade of a pocketknife.
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Photo 2: Remove the handle screw
Remove the handle screw. Then wiggle the handle and pull it off. If the handle doesn't come off, heat it with a hair dryer to free it. Be careful; if you pull too hard, it'll break.
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Photo 3: Pop loose the handle
Turn the handle screw about halfway back into the stem. Position the handle puller's post against the screwhead and press the arms together behind the handle. Turn the post clockwise until the handle pops loose. Remove the handle screw and handle. Then pull off or unscrew the escutcheon plate.
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Photo 4: Remove the stem
Slide the bath socket onto the stem bonnet and turn it counterclockwise to break the stem loose. If it sticks, soak it with penetrating lubricant. Unscrew and remove the stem.
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Photo 5: Use a seat wrench
Press the seat wrench firmly into the center of the seat. Turn counterclockwise to snap the seat loose and remove it. If it sticks, soak it with penetrating lubricant. Coat the threads of the new seat with pipe dope and screw it into the fixture body with the seat wrench.
Removing the faucet handle is the toughest part of the job. Over time, corrosion can virtually weld the handle to the stem. Remove the handle by following the instructions in Photos 1 and 2. If the handle won't come off, don't force it—it might break. Instead, remove it with a special handle puller (Photo 3). Once the handles off, unscrew the escutcheon and stem assembly (Photo 4 and Fig. A). The stem assembly controls the amount and temperature of the water dispensed through the tub spout or shower head. Remove it with a special bath socket wrench, which looks like a spark plug wrench on steroids (Photo 4).
Leaks usually occur for two reasons. Over time, the seat washer stiffens and won't seal tightly. And water pressure gradually erodes the brass rim of the seat (Photo 5). Replace the seat using a special seat wrench as shown in Photo 5.
Step 3: Replace the stem parts
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Figure A: Stem assemble and replacement parts
Fig. A shows the stem replacement parts and how to prepare the stem for reinstallation. Lubricate the parts with special plumber's grease. If you're working on a two-handled faucet, we recommend replacing the washers and seats in both the hot and cold valves.
First, unscrew the packing nut. Twist the stem clockwise and back it out of the bonnet. Pry out the old packing washer with a small flat-blade screwdriver or pick. Grease the stem threads and reinstall the stem in the bonnet. Grease the new packing washer and slide it in place, and then grease the packing nut threads and firmly tighten the packing nut. Use special plumber's grease.
Second, remove the old seat washer screw and the old seat washer. Grease the new seat washer and the threads of the new screw and then reinstall them.
Third, pull off the old bonnet washer, grease the new one and slide it in place.
Fourth, apply pipe joint compound to the bonnet threads and reinstall it in the faucet body (Photo 4).
Five, grease the handle splines and replace the escutcheon and handle.