Introduction

Ever been asked to swap a tap or fix a mixer and realised there’s no isolation valve in sight? You either drain the whole system and lose an hour (or two), or you work wet and risk a mess. There’s a better way. This guide shows you, step-by-step, how to retrofit isolation valves on copper and PEX with minimal water-off time, using practical methods that work in occupied homes. We’ll cover when it’s worth doing, how to plan a controlled stop, the tools and techniques that avoid a full drain-down, quality checks, and simple pricing logic. You’ll finish with a clean job, less disruption, and a client who calls you back.

Table of Contents

• Key Takeaways
• When and Where Isolation Valves Make Sense
• Plan the Shutoff Without Draining Down
• Step-by-Step: Copper and PEX
• Dealing With Live Drips
• Quality Checks and Client Communication
• Pricing and Timeframes
• Frequently Asked Questions
• Conclusion

Key Takeaways

• Adding isolation valves locally often cuts water‑off time from an hour to under 15 minutes on small jobs.
• In general, full drain‑down and refill on a two‑storey vented system takes 45–120 minutes; local isolation avoids most of this.
• Aerosol pipe freezing commonly gives 30–45 minutes of working time; electric kits can extend this to around an hour.
• In general, reduced‑bore service valves can drop flow by 10–20% versus full‑bore designs; choose full‑bore where space allows.
• Installing valves at each fixture commonly saves 30–60 minutes on future call‑outs and reduces callbacks caused by rushed wet work.

When and Where Isolation Valves Make Sense

Problem

Many homes lack service valves at basins, WCs, and kitchen taps. That means every minor fix becomes a whole‑house event: draining down, trapped air, and annoyed homeowners. It’s common for contractors to avoid fitting valves because the original task “is only a 10‑minute job” — until it isn’t.

Solution

Fit full‑bore, quarter‑turn isolation valves at fixture branches and appliances whenever you touch that run. Prioritise:

• Kitchen hot and cold to the mixer (often 15 mm in the UK).
• Basin feeds, WC fill valves, dishwasher and washing machine feeds.
• Bath/shower mixers (sometimes 22 mm, check before you cut).

Use WRAS‑approved valves. Full‑bore valves maintain flow; slotted screwdriver service valves are compact but can throttle. In general, UK mains pressure sits around 2–4 bar, so the difference is noticeable at taps with aerators.

Example

You’re swapping a kitchen mixer. Add two full‑bore isolators under the sink. Next time the client calls about a cartridge, you’re in and out in 15 minutes with the rest of the house undisturbed.

Plan the Shutoff Without Draining Down

Problem

Cutting into a live line, even with the stop tap shut, often means residual water dribbling from upstairs branches or tanks. That steady trickle stops you making a clean, dry joint.

Solution

Pick a method that controls= water locally so you avoid a full drain‑down.

Planning Checks

• Confirm system type: mains‑fed combi, unvented (Building Regs G3 competence required), or vented with tanks.
• Identify and test the internal stop tap and, if present, branch valves.
• Open the nearest tap downstream to break vacuum and reduce drips.

Example

WC fill valve swap with no local isolator. Shut internal stop tap. Bung the storage cistern. Crack the compression, let a cup of water out to relieve pressure, then freeze the 15 mm feed below the valve. Fit a new isolation valve and fill valve, unfreeze, test. Water‑off time: roughly 10 minutes.

Step-by-Step: Copper and PEX

Problem

Working wet or rushing compression joints when a trickle won’t stop causes weeps and callbacks.

Solution

Follow a clean, controlled sequence. The goal is a dry cut and a calm install.

Copper: Add a Full‑Bore Isolation Valve (15 or 22 mm)

1. Shut water and choose control method (freeze or local drain). Confirm zero flow at the open tap.
2. Mark and cut: allow enough straight pipe for the valve and olives. Use a sharp pipe cutter for a square cut.
3. Deburr and clean: internal deburr to protect washers; external clean for good sealing.
4. Dry fit and alignment: ensure handle clearance and correct flow orientation if marked.
5. Compression assembly: finger‑tighten both nuts, then tighten each about 1 to 1.5 turns. In general, that rule of thumb seats olives without crushing.
6. Re‑pressurise slowly; check for weeps. Quarter‑turn a flat to nip up if needed.

Technical Details

• In general, use brass olives on copper; avoid reusing old olives unless you must, and only with sealant as a last resort.
• PTFE on compression threads is not a seal; if used, it’s only as a lubricant. The olive does the sealing.
• Full‑bore valves reduce perceived throttling compared with slotted service valves; in general, reduced‑bore service valves can drop flow by 10–20%.

PEX: Add an Isolation Valve Safely

1. Confirm pipe brand and required inserts. Use manufacturer‑approved liners.
2. Control water with freezing upstream (if permitted on that material) or a temporary push‑fit stop end to create a dry section.
3. Cut square with PEX shears; de‑burr if required by the system.
4. Fit valve using compatible push‑fit or compression transition; ensure proper pipe support and no twist.
5. Re‑pressurise and check for creep at the joint. Support pipe within the recommended distance to prevent stress.

Technical Details

• Many push‑fit systems allow short‑term freezing on copper sections only; check the manufacturer before freezing plastic.
• Keep PEX away from heat sources and protect from UV if exposed in a cupboard with lighting.

Example

Kitchen sink with short, kinked PEX tails. Shut the internal stop tap, open the kitchen tap to drain. Fit temporary push‑fit stop ends to tame drips, then re‑cut and install two compact full‑bore isolators with proper PEX inserts and support clips. Result: tidy, serviceable pipework and no callbacks.

Dealing With Live Drips

Problem

Even after shutting off, you sometimes face a persistent trickle — from upstairs branches, vented tanks, or back‑syphon.

Solution

Use one or a combination of these:

• Open a lower tap and leave it running to divert residual drips away from your cut point.
• Freeze upstream on copper to create a solid ice plug and buy working time. Monitor the freeze point.
• For vented systems, bung the F&E or WC cistern (dedicated bungs) to stop gravity feed. Do not bung sealed or unvented systems.
• Use absorbent matting and a wet‑vac. A dry work area is faster than fighting drips.

Safety and Compliance Notes

• Unvented hot water: follow manufacturer instructions and relevant competence (in England and Wales, G3 requirements apply). Do not attempt makeshift isolation.
• Heating circuits on sealed systems: avoid freezing unless trained and insured for that work. Expansion and pressure can be hazardous.

Example

Basin cold feed in a top‑floor flat with a slow back‑feed. You freeze 30 cm upstream, cut, install a full‑bore isolator, then thaw and test. Total water‑off: under 15 minutes; working time on freeze: about 35 minutes with an aerosol kit.

Quality Checks and Client Communication

Problem

Small weeps show up after you’ve packed up. Clients don’t see the value if all they remember is “the water was off for ages”.

Solution

Build in five minutes of QA and clear, simple client notes.

Testing

• Pressurise slowly and wipe joints with tissue to spot weeps.
• Cycle the valve fully open/closed three times to seat seals.
• Flush aerators for debris. Clear any flow restrictors.

Documentation and Next Steps

• Take two quick photos: before/after, and valve orientation. Many contractors find these photos prevent disputes and help the next tech.
• Leave the client with plain‑English instructions: “If you need to change the tap cartridge, turn these handles 90 degrees.”

Speed Up Your Paperwork

If you like to finish admin before you leave, capture the work with a quick voice note and a couple of photos, generate a professional proposal or work confirmation, get a digital signature, and convert it to an invoice when accepted — all without retyping. With Donizo, you can:

• Speak the scope, add text and photos, and get a branded PDF proposal fast.
• Send it for e‑signature via a client portal and move from acceptance to invoice in one click.
• Track payments without jumping between tools.

Contractors often report this saves 15–30 minutes per small job and halves the back‑and‑forth.

Pricing and Timeframes

Problem

It’s easy to under‑quote “just two valves under the sink”, then lose your day to drain‑downs and callbacks.

Solution

Price for speed and certainty, not just parts.

• Time: In general, a straightforward under‑sink pair takes 30–60 minutes with local isolation; a bath mixer branch can take 45–90 minutes depending on access.
• Control method: Allow an extra 10–15 minutes to set and monitor a freeze point; less with a clean local drain on a vented line.
• Parts: Full‑bore valves cost more than slotted service valves but maintain flow and reduce complaints. That small premium pays back quickly.
• Future value: Make clear that valves reduce future water‑off time by 30–60 minutes on typical call‑outs.

Example

Quote line items like this:

• “Fit two WRAS‑approved full‑bore isolation valves to kitchen hot and cold. Includes controlled shutdown, testing, and photo documentation.”
• Add an optional line for “Replace flexible hoses (if aged or corroded)”, so you protect the job from old tails failing post‑works.

Frequently Asked Questions

Can I Freeze Plastic (PEX) Lines?

In general, freeze copper upstream rather than the plastic itself. Some systems permit plastic freezing with specific sleeves, but you should follow the pipe manufacturer’s guidance. Safer route: create a dry section with temporary push‑fit stop ends on the plastic, or freeze on the copper branch before the plastic.

Which Isolation Valve Should I Choose?

Use WRAS‑approved, full‑bore quarter‑turn valves where space allows. In general, reduced‑bore service valves can drop flow by 10–20% compared with full‑bore. For tight spaces behind basins, compact screwdriver‑slot valves are acceptable, but explain the flow impact to clients.

My Compression Joint Is Weeping — What Now?

Back off slightly, re‑align, and re‑tighten a flat at a time. Ensure the pipe is deburred and fully seated. If the olive or pipe is marked or out‑of‑round, replace the olive. A common rule of thumb is 1 to 1.5 turns after finger‑tight from new; avoid overtightening.

Do I Need to Drain a Combi System to Fit Valves on Taps?

No. Tap supplies are on the mains cold and hot side of the combi plate heat exchanger. Shut the internal stop tap and use a local isolation method. Heating circuits are separate and sealed; do not bung or freeze them unless trained and insured for that work.

Is It Safe to Bung Tanks?

Only on vented systems and with proper bungs. Do not bung unvented or sealed systems. For unvented cylinders, follow the manufacturer’s isolation procedure and relevant competence (G3 in England and Wales).

Conclusion

Adding isolation valves the smart way turns “messy 10‑minute jobs” into tidy, profitable small works. Plan your shutdown, control the water locally, fit full‑bore valves, and spend five minutes on QA. You’ll cut water‑off time dramatically, avoid callbacks, and leave the site better than you found it.

Want the paperwork done before you start the van? Speak the scope, snap a photo, and send a branded proposal with e‑signature right away using Donizo. When the client signs, convert it to an invoice in one click and keep payment status in view. That’s how you save time on admin and get back to the next job.