Prep bathroom plumbing (before renovation)
Save £100–300 in under 90 mins — no plumber needed
Most people call a plumber just to disconnect a basin and cap some pipes. This is straightforward prep work — and doing it yourself means you understand exactly what you are passing to the next phase.
Last updated: June 2025
Only basic tools needed — most homes already have them.
Before you start
This guide covers basic plumbing prep only — isolating, disconnecting, and capping. It does not cover moving pipes, installing new supply runs, or working with the boiler.
You will need the water supply turned off before any connections are opened. Know where your stop cock is before you start.
Be aware of pipes hidden inside walls or under floors — this guide is for exposed supply and waste pipes under a basin or behind a toilet.
If you rent, get written permission before disconnecting any plumbing — see the renter notice below.
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Tools & materials
- ✓Adjustable spanner— for compression fittings and tap connections
- ✓Bucket— catch residual water from disconnected pipes
- ✓Rubber gloves— keep your hands dry and protected
- ✓Sponge / cloths— mop up drips before they spread
- !PTFE tape— buy from any hardware shop — cheap and essential
- !Push-fit blanking caps— to seal open pipe ends safely
Want everything in one go?
Prices shown on retailer sites. Always check current pricing before purchasing.
Turn off the water supply
Find the isolation valves on the hot and cold supply pipes under the basin or behind the toilet. Turn each valve 90 degrees so the slot sits across the pipe — that means closed. If there are no isolation valves, turn off the main stop cock (usually under the kitchen sink or where the water enters the house). Why: any water still in the system under pressure will spray out the moment you loosen a connection. Isolating first keeps you in control.
Most people get this done in under 5 minutes.
Quick guides for this phase
Where beginners go wrong
Not fully isolating the water. Turning an isolation valve halfway is not off. The slot must sit across the pipe — at 90 degrees to the pipe run. Always confirm by opening the tap and waiting for the flow to stop completely.
Over-tightening compression fittings. Compression fittings seal by squashing a small olive ring — not by brute force. Finger-tight plus one quarter turn with a spanner is enough. Going further deforms the olive and creates leaks rather than preventing them.
Ignoring slow drips from capped pipes. A drip that looks minor now is water under pressure finding the weakest point. Check every capped end before moving on. A dripping cap means the cap is not fully seated or the pipe end is damaged.
Stop and call a plumber if...
The pipes run inside the wall and you cannot access the fittings without opening up the structure
A leak does not stop after capping — water is finding a path through a corroded or cracked section
You find green or white powdery corrosion on copper pipes — pitting corrosion means the pipe wall is compromised
The main stop cock will not close fully — do not proceed until the water can be properly isolated
Cost breakdown
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 confidently isolate a water system, disconnect supply connections without flooding the room, and leave exposed pipe ends safely capped and ready for the next phase.
More importantly, you know how to check your work — confirming the isolation holds and the caps are seated — before moving on. That is the habit that separates a successful DIY renovation from an expensive callback.
This unlocks:
Continue your renovation
Most people would call a plumber for this prep work.
⚠️ Watch out if you rent
Bathroom plumbing work in a rented property requires your landlord's written permission. Only disconnect existing fittings if you have confirmed written agreement that the bathroom is being renovated. Keep a record of every change you make.