Cap off a pipe temporarily
15–20 minutes — leave pipes safe while renovation continues
After disconnecting a basin or removing a fixture, exposed pipe ends need capping so the water supply can be restored while other work continues. This is how to do it properly.
Last updated: June 2025
Only basic tools needed — most homes already have them.
Part of the Bathroom Renovation project
This is a Phase 2: Plumbing Prep skill in the full bathroom renovation walkthrough.
If you're renovating your bathroom, start here →Before you start
This guide covers capping standard 15mm and 22mm domestic water supply pipes — the pipes that feed basins, toilets, and showers. It does not cover soil pipes, waste pipes, or gas pipes.
You will need to know whether your pipes are copper or plastic before buying caps. The two types of cap fitting are different and not interchangeable.
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Tools & materials
- ✓Adjustable spanner— for tightening compression fittings
- ✓PTFE tape— for threaded cap connections
- ✓Bucket— to catch residual water from the pipe
- ✓Cloths— for mopping up and checking for drips
- !Pipe caps (correct type and size)— compression for copper, push-fit for plastic — buy both 15mm and 22mm
Want everything in one go?
Prices shown on retailer sites. Always check current pricing before purchasing.
Isolate the water supply and drain the pipe
Close the relevant isolation valve — the slot must sit across the pipe, at 90 degrees to the pipe run. Confirm it is fully closed by opening the nearest tap and waiting for flow to stop completely. Once isolated, open the lowest tap on that circuit (often a kitchen tap on the same run) to drain any remaining water from the pipe length. Have a bucket and cloth ready under the pipe end before you proceed. Why: even with the isolation valve closed, there is water sitting in the pipe between the valve and the open end. Draining it before you cap means you are fitting the cap onto a dry pipe end rather than fighting water pressure as you work.
Most people get this done in under 5 minutes.
Where beginners go wrong
Using the wrong cap type. Compression caps on plastic pipe (without a copper liner insert) will cut into the plastic and fail under pressure. Push-fit caps on copper that is not compatible with the system brand will not grip. Match cap to pipe.
Not draining the pipe before capping. Fitting a cap with water pressure behind it is difficult — the pressure pushes against the fitting as you try to tighten it. Drain the pipe first by opening a lower tap on the same circuit.
Treating a drip as acceptable. A drip under first pressure becomes a flow as the system heats up. A correctly fitted cap is dry immediately. If it drips, re-fit it.
Stop and call a plumber if...
The pipe end is corroded, pitted, or deformed — a damaged pipe end will not seal reliably and the pipe needs cutting back to clean material
You cannot identify the pipe type or the correct cap to use — buying the wrong fitting and forcing it is worse than leaving the water off while you get advice
Any cap drips after re-fitting — do not leave a pressurised dripping cap unattended overnight
Recommended starter kit
Five tools that cover most home repairs.
- →Adjustable spannerAmazon·Screwfix
- →Screwdriver setAmazon·Screwfix
- →PTFE tapeAmazon·Screwfix
- →Spirit levelAmazon·Screwfix
- →Tape measureAmazon·Screwfix
Want everything in one go? Get it on Amazon
What you just learned
You can now safely cap off a water supply pipe — the right fitting for the pipe type, fitted correctly and tested under pressure. This means you can restore the water supply to the rest of the house while bathroom work continues, rather than leaving the whole supply off.
This unlocks:
⚠️ Watch out if you rent
Capping a pipe temporarily during a bathroom renovation requires your landlord's written permission if you are doing the wider renovation yourself. If a landlord-authorised plumber is doing the work, they will handle this. Do not cap pipes without the landlord knowing — they need to be aware the supply is modified.