PLUMBING

Cap off an unused pipe

Cut back, cap and secure a redundant water pipe safely, choosing the right fixing for your wall type.

CP-01Confirm the pipe is dead and plan the cutTrace the pipe back to what it used to feed, and make sure it isn't part of a loop or vent that other fittings still rely on. Decide where you'll cut it — as close as you reasonably can to the nearest live tee, rather than leaving a long disused stub. Take a photo of the run before you disturb it, in case you need to explain the layout later.
RULES
KNOW THE RULES

The Water Supply (Water Fittings) Regulations 1999 discourage long disused pipe sections (dead legs), because stagnant water in them can affect water quality. Cut back as close as you can to the live pipework rather than just capping a long stub.

CP-02Gather your tools and materialsCheck whether the pipe is copper or plastic, because the cap and joint method differ. Lay dust sheets under the work area, since a little water will still drain out even after isolating. Keep a bucket and old cloth handy for drips.
1 each · Dust sheet
1 each · Small bucket
1 each · Old cloth or rag
CP-03Isolate the water and drain the pipeShut off the isolation valve feeding this pipe, or the main stopcock if there's no local valve. Open the cut point or a nearby tap on the same run and let any remaining water drain into the bucket. Mop up drips before you carry on.
CP-04Cut the pipe back and deburr the endCut the pipe square at the point you chose earlier, using a pipe cutter for copper or plastic pipe shears for plastic. Remove any burr or swarf from the cut edge with a file or the reamer on your cutter, so the new joint seals properly. Wipe the pipe end clean and dry before fitting anything.
1 each · Emery cloth or wire wool
CP-05Fit the end capFor copper pipe, slide on the compression cap, fit the olive, and tighten the nut with two spanners until snug plus a quarter turn — don't overtighten or you'll damage the olive. For plastic push-fit pipe, push the stop end on firmly until it clicks and won't pull back off. Check the cap sits square, not skewed, before you move on.
1 each · Compression end cap 15mm (copper)
1 each · Push-fit stop end 15mm (plastic)
1 roll · PTFE tape
CP-06Secure the capped stub to the wallBefore you drill, run a cable and pipe detector over the spot, then still treat it as if something could be there — detectors miss deep cables, metal-backed board, and anything outside the usual zones. Check your stopcock is off and turns freely before you start; if you have any doubt about what's behind the wall, isolate the circuit at the consumer unit first. Tap the wall: solid brick or block sounds dead and solid, a stud wall sounds hollow between the studs. Run a stud detector or a magnet across the wall to find the fixings holding the board on — a pilot hole brings out fine dust from a timber stud, or fine metal swarf from a metal one. In solid brick or block, drill a 6mm hole 35-40mm deep, fit a wall plug, then screw the clip on with a 30mm woodscrew. Into a timber stud, screw straight into the centre of the stud with a 30mm woodscrew, no plug needed. Into a metal stud, use a self-drilling metal-stud screw or a small rated toggle fixing — never a plain plastic plug or ordinary woodscrew, both strip straight through 0.5mm steel. On dot-and-dab plasterboard, use a fixing long enough to pass through the board and the dab void and bite into the masonry behind, typically 50-60mm. On lath and plaster, find the timber stud or joist behind the laths and fix into that, since the lath alone can crumble under load.
1 each · Pipe clip 15mm
2 each · Wall plug (masonry)
2 each · Woodscrew 30mm
2 each · Self-drilling metal-stud fixing
2 each · Hollow-wall toggle fixing
CP-07Turn the water back on and test for leaksTurn the isolation valve or stopcock back on slowly and check the new cap for drips straight away. Run your hand around the joint and the pipe clip fixing to check for dampness. Leave it ten minutes and check again, since some leaks only show once the pipe is at full pressure.
CP-08Make good and tidy upFill any wall holes made for access or fixings with a suitable filler and leave to dry before sanding smooth. Dispose of the old fitting, offcut pipe and packaging responsibly. Wipe down your tools and work area, and fold away the dust sheet.
1 each · Filler tube
1 sheet · Fine sandpaper

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