Replace a leaking stopcock

Isolate the water supply, remove the leaking stopcock, fit a new one, then check for leaks and tidy up.

RS-01Buy the right stopcock and fittingsCheck the pipe size feeding your stopcock — almost always 15mm in a UK home. Buy a matching stopcock, two compression fittings if you're cutting the pipe back, and PTFE tape. Clear the cupboard under the sink so you've got full access before you start.

1 each · 15mm compression stopcock

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1 roll · PTFE tape

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2 each · Compression coupling

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RS-02Find every isolation point in the houseFind your internal stopcock, usually under the kitchen sink, and check it actually turns — you're about to replace it, so it may not fully shut off. Also find your external stopcock if you have one, usually under a small cover near the boundary of your property, and turn it with a stopcock key. If there's no working outside stopcock, tell your household the water will be off for the whole job.

1 each · Stopcock key

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RS-03Turn off the water and drain the pipesClose the stopcock fully — internal, external, or both if you have them. Open the kitchen cold tap and every other tap in the house, starting with the highest and finishing with the lowest, to drain the pipework and relieve pressure. Flush toilets to empty the cisterns and leave taps open until nothing comes out.

RS-04Protect the area and catch trapped waterLay towels or a dust sheet under the stopcock and place a bucket beneath it — there's always some water left in the pipe even once it's drained. If there's a socket close to the work area, for example under the sink for a waste disposal unit, switch off that circuit at the consumer unit first in case of drips.

1 each · Bucket

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RS-05Remove the old stopcockUndo the compression nuts on each side using two adjustable spanners — one to hold the fitting steady, one to turn the nut. Let any trapped water drain into the bucket. If the fitting won't budge or the joints are soldered, cut the pipe cleanly on each side instead, leaving enough spare pipe to fit new couplings.

2 each · Spare compression olive and nut

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RS-06Fit the new stopcockCheck the arrow on the body of the stopcock — it must point away from the mains, towards the tap. Slide a new nut and olive onto each pipe end, push the pipe fully into the stopcock, then tighten by hand and finish with a quarter turn of the spanner. Don't overtighten, as this can split the olive and cause a leak.

RULES

1 roll · PTFE tape

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KNOW THE RULES

Any fitting used on your mains water supply must comply with the Water Supply (Water Fittings) Regulations 1999 — buy a stopcock that's WRAS-approved for drinking water use.

RS-07Support the pipework against the wallBefore you drill, use a cable and pipe detector, but don't trust it completely — detectors miss deep cables, cables in metal conduit, and pipes behind metal-backed plasterboard, and metal stud frames confuse cheap detectors further. Water should already be off from earlier steps, but if there's any doubt about hitting an electrical cable, isolate the circuit at the consumer unit before drilling. Work out your wall type first: tap the wall — solid masonry sounds dead all over, a stud wall sounds hollow between studs and solid on the stud line, and a stud detector or magnet (which tracks screw heads under plasterboard) will confirm the line. A small pilot hole tells you the stud material: fine pale dust is timber, fine grey swarf is metal.

1 each · Cable, pipe and stud detector

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4 each · Plastic pipe clip (15mm)

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1 pack · Rawlplug wall plug pack

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1 pack · Screws, 30mm

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4 each · Metal-stud self-drilling fixing

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4 each · Long fixing for dot-and-dab (60-75mm)

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RS-07bChoose the right fixing for your wall typeSolid brick or block: drill to the plug's depth (usually 6-7mm), fit a Rawlplug, then screw the pipe clip in place. Plasterboard on timber studs: drive the screw into the centre of the stud, not just the board. Plasterboard on metal studs: use a self-drilling metal-stud screw or a hollow-wall toggle fixing — never a plastic wall plug or an ordinary wood screw, both strip straight through 0.5mm steel. Dot-and-dab plasterboard: use a long fixing (60-75mm) that passes through the board and adhesive dabs into the masonry behind. Lath and plaster: work slowly to avoid cracking the plaster, and fix into a timber lath or batten behind if you can find one. A metal stud alone won't hold anything heavy or anything that pulls on the wall — for a bracket carrying real weight, fit through to the masonry or add a timber noggin between the studs instead.

RS-08Turn the water back on and check for leaksOpen the stopcock slowly — opening it fast can cause a bang (water hammer) and stress the new joints. Check every joint you've touched for drips, especially the compression fittings on the new stopcock. Run the kitchen tap for a minute to clear trapped air, then check the joints again after 10 minutes under full pressure.

RS-09Tidy up and finishDry the pipework and cupboard, and dispose of the old stopcock — the metal parts can usually go in scrap or metal recycling. Turn any isolated circuits back on at the consumer unit. Keep a note of the new stopcock's size and make in case you ever need a replacement washer.

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