This guide is based for Australians, so products/terminology/plumbing standards may differ in your region. Please obey your local regulations when it comes to working on plumbing (as stupid as they may be) and I take no responsibility for any damage caused from following this guide.
1. Assessment.
What is wrong with the tap, is it leaking out of the body washer, is the letting water run through the spout, is it coming up through the spindle when the water is running, is it stiff or do you need too much pressure to turn it off.
2. Disconnect Supply
Turn off the supply at the mains, as well as the supply from the hot water system (may as well do both taps at the same time).
3. Dis-assembly (Assuming a tap with all of the problems above)
Remove the button that holds the handle onto the spindle. May have to use some sort of pliers/channel locks depending on the design. Open the tap fully (can do that before button removal if you want). Remove the handle and then unscrew the shroud over the spindle by hand, or using some sort of clamp/tool over a cloth to protect it.
Use a correctly sized shifting spanner to remove the spindle body.
4. Inspect
Shine a flashlight down the tap, inspect the brass seat, and feel the thickness remaining with a hooked tipped tool (like a dentist’s). Spin the spindle back down in your hand to feel how well it moves, and inspect the black o-ring as well as the orange/red body washer.
5. The Seat
Pull out the old valve with needle nose pliers. Be sure not to damage the threads on the tap body.
Assuming the seat is warped/chipped, use a drill powered reseating milling tool (stored in a oily rag for physical and corrosive protection) to reseat. Pull the spindle of the reseating tool up and clamp it with a small plastic spring loaded clamp or something similar to hold it UP away from the seat, then screw in the tool to the tap body and tighten gently with a shifting spanner.
IMPORTANT: If you have one of those hand turned seating tools, cut off the T bit on the handle, and tie some fishing line to the end of it. You now have a plumb level. That’s all it’s good for.
Attach your drill to the bit and remove the clamp while holding it up (Don’t let it strike the seat while not moving) and start the drill up (What speed / RPM should I use). While the tool is spinning, slowly press it down and apply gentle pressure. The length of time this takes is a guess, but it’s best to be conservative and to it three or four short times, than one big go and destroy your seat.
While the tool is still spinning, lift away from the seat and then stop the drill. Remove the drill, clamp the spindle in place then remove the tool from the tap body with a spanner.
Inspect the seat, I like to see clean fresh uniform brass, on at least 80% of the seat with no chips/cracks. Usually the latent pressure left in the taps is enough to force the brass filings out.
6. The Valve
Commonly called a washer, this is the plastic/metal thing you buy from bunnings that actually forms a seal against the seat to stop water coming through your spouts.
I use Hydroseal. You can get them in a pack of 10 for $20 at Bunnings (Always buy in bulk to save money in the long term).
I usually insert this into the tap by hand and push down with my finger to make sure it’s sitting flush, it should stop the water dribbling through. Depending on your spindle height you may need to use a rubber spacer.
7. The Spindle
I usually pull off the O-rings because they’re cheap (buy in bulk), as well as the body washer. I then clean the threads/body with either light sand paper or wire brushes shaped like toothbrushes. Then I rinse it in a bucket of water standing buy. I will also apply plumbing grade silicone lubricant to the spindle, along the entire length (you will need to turn the spindle up and down to get access to all of it.). Then I will soak the body washer in clean water and replace that.
Some spindles can be fully removed removed from their housing, if you can do this I would recommend it. Then I use a spindle thread cleaning tool (cost about $6 from Bunnings, get the Doust brand) on the inside of the spindle housing to push out all the gunk.
8. Re-assembly
‘Open’ the spindle, then attach it back to the body, aligning it with the valve that I left in place. You shouldn’t use plumbing tape on a spindle assembly as that’s what the red body face washer is for. Screw in by hand (it should go easily, that’s what the cleaning was for), and then tighten with a 20-30cm shifting spanner.
Close the tap, temporarily attaching the handle to the spindle to do so. If you have someone else with you, get them to turn the water mains back on but make sure you can communicate with them quickly in case you did something wrong and you end up blasting a jet of water across your bathroom (Guess how I learnt to do this ;) ).
Assuming the tap turns smoothly, and stops water flow with a easy turn (Be aware that the spouts especially showerheads will still dribble for a bit. This is normal as it’s just air coming up through the spout and letting water come out) reattach the shroud and handle and screw on button.
9. Clean up.
Wipe down the taps with a clean dry cloth, maybe a bit of spray and wipe, as well as the floor and your boot marks you left in the bathtub. Dry and clean your tools with an oily rag, store your seating tool safely. Pack everything up and then educate your family/housemates to never over tighten taps again.
