Introduction
Leaks, callbacks, and chewed-up olives—most of us have seen the fallout from a rushed flexi connection. If you want rock-solid, leak-free results, you need The correct way to connect a flexi to isolation valve! This guide shows you exactly how: the parts to use, the order to fit them, what to tighten (and what not to), and how to commission the line without drama. Follow these steps and you’ll avoid weeps, kinks, and flow issues on day one and day 100.
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Quick Answer: The correct way to connect a flexi to isolation valve! is to fit a full-bore 15 mm isolation valve (arrow towards the outlet), prepare the pipe, tighten the compression joint hand-tight plus 1/4–1/2 turn, then attach the flexi’s 1/2 inch BSPP female with a new washer—hand-tight plus 1/4 turn. Open and test for 2–5 minutes at working pressure.
Table of Contents
Key Takeaways
- Use a full-bore 15 mm isolation valve with the flow arrow pointing towards the flexi; aim for a minimum bend radius of 50–75 mm on the hose.
- Compression joints: tighten hand-tight plus 1/4–1/2 turn; flexi face-seal joints: hand-tight plus about 1/4 turn—no PTFE on face-seal threads.
- Always fit a new EPDM or fibre washer on 1/2 inch BSPP tap connectors; never double up washers.
- Clip and support the pipe within about 150 mm of the valve, and avoid twisting the braid when tightening.
- Pressure test for 2–5 minutes, recheck after 30 minutes and again within 24 hours.
Getting The correct way to connect a flexi to isolation valve! starts with the right kit.
- Full-bore isolation valve (15 mm compression both ends, or 15 mm x tap connector as required). Flow arrow must point to the outlet.
- WRAS-approved braided flexi hose in the correct sizes (commonly 1/2 inch BSPP female x 15 mm, length 300–500 mm; check minimum bend radius from manufacturer, typically 50–75 mm).
- New EPDM or fibre sealing washer for BSPP female ends (1 per joint).
- Copper or plastic pipe (15 mm typical). If plastic, use manufacturer-approved pipe inserts/stiffeners.
- Spanners: adjustable plus 15–22 mm open-ended set. Two spanners make life easier.
- PTFE tape or jointing compound only if you have tapered male threads elsewhere—never on face-seal BSPP with washer, and not on compression threads. A light smear of potable jointing compound on the olive is optional.
- Pipe slice/deburrer, tape measure, pipe clips, and a small torch for inspection.
Tip: Many contractors find keeping 300 mm and 500 mm hoses in the van covers 80–90% of tap and appliance runs.
Step-by-Step: The correct way to connect a flexi to isolation valve!
Follow this sequence to nail The correct way to connect a flexi to isolation valve! every time.
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Isolate and Drain
- Shut the main stopcock or upstream valve and crack a downstream tap to relieve pressure. Expect 100–300 ml of residual water from the line.
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Position the Valve Correctly
- Fit the isolation valve with the arrow pointing towards the outlet (towards the flexi). Keep the screwdriver slot or lever accessible. Aim for at least 100 mm of straight pipe before and after where practical.
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Prepare the Pipe
- Cut square with a pipe slice. Deburr inside and out. For plastic, insert a proper pipe stiffener. Clean the pipe and ensure no paint, burrs, or scoring where the olive seats.
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Make the Compression Joint to the Pipe
- Slide the compression nut and olive onto the pipe. Offer the valve up square. Hand-tighten the nut, then use two spanners to tighten a further 1/4–1/2 turn. You’re compressing the olive onto the pipe—not “chasing” threads. Don’t use PTFE on compression threads; a tiny smear of potable jointing compound on the olive is optional.
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Support and Clip
- Add a pipe clip within about 150 mm of the valve to prevent movement. Good support reduces stressing the flexi and extends service life.
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Check Flexi Orientation and Length
- Select a flexi that reaches comfortably without stretching or forcing a tight bend. Keep bends gentle—respect the 50–75 mm minimum radius. Ensure the hose won’t rub on sharp edges or hot components. Avoid heat sources exceeding the flexi’s rating (often 85°C).
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Fit the Flexi to the Isolation Valve Outlet
- For a 1/2 inch BSPP female flexi end: ensure a new washer is seated flat in the swivel nut. Offer up square, hand-tighten until the washer contacts, then nip up 1/4 turn with a spanner. Do not use PTFE on a face-seal joint with a washer.
- Reinspect after 30 minutes and again within 24 hours. Fit protective grommets or edge guards where hoses pass through cabinetry. Ensure the valve is fully open for normal use.
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Common Mistakes to Avoid
- Using PTFE on face-seal joints: The washer does the sealing on 1/2 inch BSPP female swivel connections. PTFE here causes mis-seating and leaks.
- Over-tightening compression: More force doesn’t mean more seal. Aim for hand-tight plus 1/4–1/2 turn. Over 3/4 turn risks crushed olives and split nuts.
- Twisting the hose: Always counter-hold the valve while tightening the flexi. Twisted braid shortens life and can hum under flow.
- Wrong size: 3/8 inch vs 1/2 inch confusion is common. Confirm thread size and type. Keep adaptors handy but use WRAS-approved parts.
- Tight bend radius: Anything less than 50–75 mm can kink the liner, throttling flow and inviting failure.
- Valve backwards: The arrow must point towards the outlet. Backwards valves can whistle, restrict flow, and trap debris.
- No support: Unclipped pipe lets the joint move. A simple clip within 150 mm reduces callbacks.
Testing, Commissioning, and Aftercare
- Cold test first: Open the isolation valve slowly and check each joint. Tissue or a dry finger under the joint shows small weeps immediately.
- Hot test second: Run hot for 1–2 minutes. Thermal expansion can loosen a borderline joint; retighten 1/8 turn if needed.
- Final flow check: Full-bore valves preserve flow. If the outlet is sluggish, confirm the valve is fully open and the hose isn’t kinked.
- Revisit: Many contractors schedule a quick recheck within 24 hours on larger jobs, especially where cabinetry hides joints.
Maintenance tip: Advise clients to operate the isolation valve twice a year. Valves left untouched can seize.
Compliance and Best Practice Notes
- Use WRAS-approved isolation valves and flexi hoses for potable water in the UK.
- Flexi hoses are consumables—many contractors proactively replace them every 5–10 years, sooner in hard water or high-use environments.
- For plastic pipe under compression fittings, always use the manufacturer’s recommended pipe insert. Without it, olives can deform the pipe and cause delayed weeps.
- Avoid dead legs and keep isolation valves accessible. Don’t bury serviceable joints behind immovable finishes.
- Hot side temperature: Many flexis are rated to about 85°C. If you’re near a cylinder or boiler outlet, confirm the rating or install a blending/mixing solution.
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FAQ
Do I need PTFE tape when connecting a flexi to an isolation valve?
No—if the flexi uses a 1/2 inch BSPP female swivel with a washer, the washer creates the seal. Do not use PTFE on face-seal threads or on compression threads. For compression joints, tighten hand-tight plus 1/4–1/2 turn. Only use sealant on tapered male threads elsewhere if specified by the fitting manufacturer.
How tight should I make the flexi connector on the valve?
For a face-seal (washered) 1/2 inch BSPP connection: go hand-tight until the washer bites, then add about 1/4 turn with a spanner. For 15 mm compression, hand-tight plus 1/4–1/2 turn is typical. If it weeps, nip a further 1/8 turn—avoid over-tightening which can crush olives or split nuts.
Which way round does the isolation valve go?
Install the valve with the flow arrow pointing towards the outlet—the direction of water travel to the flexi and fixture. Backwards installation can restrict flow, cause noise, and trap debris. Keep the lever or screwdriver slot accessible for future isolation and maintenance.
Can I connect a flexi to plastic pipe using a compression isolation valve?
Yes, but you must use the correct pipe insert/stiffener for the plastic pipe brand and size. Prepare the pipe clean and square, then tighten the compression joint hand-tight plus 1/4–1/2 turn. Support the pipe within about 150 mm of the valve to prevent movement and future weeps.
What size is the thread on a typical flexi tap connector?
Most UK tap flexis use a 1/2 inch BSPP female swivel with a flat sealing washer for connecting to valves or tap connectors. Monobloc tap tails can be 3/8 inch, M10, or M12, so you may need the correct adaptor or a flexi with matching ends. Always confirm sizes before installation.
Conclusion
You now have The correct way to connect a flexi to isolation valve! down to a repeatable process: correct valve orientation, clean pipe prep, the right washer, controlled torque (1/4–1/2 turn), proper support within 150 mm, and a thorough 2–5 minute test with a 30-minute and 24-hour recheck. Document this as your team standard to cut callbacks and save hours each month.
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