Replacing the base seal on a tap that drips from underneath

How to tell the fault is in the base, not the spout

Dry the whole tap and the area around it thoroughly, then run water and watch closely. A spout leak drips from the tip or gathers under the spout opening. A base leak appears as a film of water spreading out from where the tap body sits on the sink, and it often shows even when the water is off, just from the tap swivelling.

Mixer taps with a swivel spout have a separate O-ring or two at the base of the spout itself, in addition to the ring sealing the whole tap unit to the sink. If the water appears only when you turn the spout from side to side, the fault is in the spout base ring rather than the main body seal, and the fix is similar but quicker.

Check underneath the sink as well. Water tracking down the tap's shank and pooling on the base of the cupboard is a sure sign of a base seal fault rather than a supply pipe or valve joint, which would show a leak lower down at the fittings.

What you need before starting

You will need an adjustable spanner or a basin wrench for the mounting nut underneath the sink, a flat screwdriver or hex key to remove the tap handle, a soft cloth, and a torch, since the space under most Estonian kitchen and bathroom sinks is cramped and poorly lit.

For the seal itself you need a replacement O-ring of the right diameter and thickness, plumber's grease (silicone-based, not petroleum jelly, which degrades rubber), and ideally the make of the tap so you can look up the correct part rather than guess.

Before touching anything, turn off the local shutoff valve under the sink. If there is no local valve, which is common in older Tallinn flats and Soviet-era panel buildings, you will need to shut off the riser or the flat's main stopcock, and it is worth having one fitted while the tap is apart so future work does not need the whole flat's water off.

• Adjustable spanner or basin wrench
• Screwdriver or hex key for the handle
• Replacement O-ring, correct size
• Plumber's silicone grease
• Torch and a cloth
• Bucket or towel for residual water

Taking the tap body apart and finding the seal

With the water off, open the tap to release pressure, then plug the sink so small parts cannot fall down the drain. Remove the handle, usually held by a grub screw under a cap or a single visible screw, then lift off any decorative cover to expose the mounting nut.

Undo the mounting nut underneath the sink and lift the tap body clear. Wipe the base and the section of the shank that sat inside the sink hole. The main O-ring sits in a groove around this shank, and on many mixers there is a second, thinner ring higher up where the spout swivels.

Take the old ring off carefully and note its condition. A ring that has gone flat, cracked, or turned brittle rather than staying rubbery has simply reached the end of its life, which on a tap that sees daily use is normal after some years rather than a sign anything was done wrong.

Finding the right O-ring and fitting it

Measure the old ring's inside diameter and its thickness (the cross-section, not the overall width) with a ruler or callipers if you have them. O-rings are sold in standard metric sizes at plumbing merchants and larger hardware shops, and taking the old one along to match against samples is more reliable than measuring alone.

Fit the new ring dry first to check it seats fully in the groove without twisting, then remove it, coat it lightly with plumber's grease, and refit it. The grease helps it seat evenly and protects it from drying out, which is often what kills the next one prematurely.

Reassemble in reverse: tap body back into the hole, mounting nut hand-tight then a quarter turn more with the spanner, handle back on. Turn the water on gradually and check the base while the tap is both off and running, and again after it has swivelled a few times.

When replacing the tap makes more sense than repairing it

If the tap is more than ten to fifteen years old, a new seal will often stop the base leak but not the next fault, since the body itself, the cartridge, and any chrome plating are ageing together. Spending an hour finding a seal for a tap that will need attention again within a year is a false economy.

Corrosion is the other sign to watch for. If the shank or the mounting nut is pitted, seized, or crumbling as you undo it, or if mineral deposits have built up so heavily inside the body that the new ring cannot seat properly, the tap is not worth chasing further.

A straightforward tap replacement is not an expensive job and removes the guesswork: from 55 € for a standard kitchen or bathroom mixer, done in one visit, with the old tap removed and the new one sealed and tested.

When it is better not to attempt this yourself

If the shutoff valve under the sink will not turn, or turns but does not stop the flow, do not force it or start dismantling the tap, since you may end up unable to stop the water at all. This is a case for a plumber before it becomes a flood.

Taps built into a stone or composite worktop, or ones with an integrated waste disposal switch or filtered water spout, are more involved to remove and refit correctly, and a wrong seal or a cracked mounting can mean redoing the work twice.

If you are not confident under the sink, or the space is too tight to work in safely, plumbing work is charged from 45 € an hour with a 25 € call-out in Tallinn that comes off the bill if the job goes ahead, and a straightforward base seal replacement is usually well within the first hour.