22mm Push-Fit Pipe: When to Use It, What to Buy, and How to Avoid Leaks

Your plumber runs 22mm pipe from the boiler to a manifold, drops to 15mm for each radiator branch, pressure tests the lot, and boards over it before you've had a chance to ask questions. Six months later, a fitting buried under your new kitchen floor weeps. The laminate bubbles. The insurer wants to know whether the pipe was barrier-rated and whether the joints were accessible. You don't know. That's the scenario this page prevents.

What it is and what it's for

22mm push-fit pipe is plastic plumbing pipe with a 22mm outside diameter, designed to carry water under pressure without soldering. You push the pipe into a fitting until it clicks, and an internal O-ring (a rubber gasket) seals watertight while a collet (a ring of stainless steel teeth) grips the pipe so it can't pull out. No flux, no blowtorch, no fire blanket behind the joint. That's the appeal.

The 22mm size handles higher flow rates than its 15mm sibling. Your plumber uses it for the main flow and return circuit on central heating systems, for the primary hot and cold distribution pipes from the cylinder or combi boiler, and for bath feeds where a 15mm pipe would restrict flow and take forever to fill. Anywhere the system needs to move a larger volume of water, 22mm is the standard domestic size.

All push-fit pipe sold for plumbing in the UK must comply with BS 7291 (the British Standard for thermoplastic pipe systems for hot and cold water supply and heating) and carry WRAS approval (Water Regulations Advisory Scheme, confirming the product is legal for use in contact with drinking water). Every branded product from JG Speedfit, Hep2O (Wavin), PolyPlumb, and Flomasta meets this. Check the print on the pipe if you're buying from a market stall or eBay. No BS 7291 marking means it's not approved.

Barrier vs non-barrier: the distinction that matters most

This is the single most common mistake homeowners make when buying push-fit pipe, and the consequences take years to show up.

Barrier pipe has a thin layer of aluminium or EVOH (ethylene vinyl alcohol, a plastic with very low oxygen permeability) bonded between the inner and outer walls. This layer stops oxygen from permeating through the plastic and dissolving into the water inside. Non-barrier pipe has no such layer.

Why does oxygen matter? In a sealed central heating circuit (the closed loop between your boiler and radiators), dissolved oxygen corrodes the steel components: radiators, the boiler heat exchanger, and steel fittings. The corrosion creates magnetite sludge (the black muck that comes out when you bleed a radiator). Sludge blocks radiator channels, reduces boiler efficiency, and eventually kills the boiler pump or heat exchanger. This doesn't happen in month one. It takes 2-5 years to become obvious, by which point the pipe is buried, the floor is down, and finding the cause is expensive.

At the builders' merchant, barrier pipe is usually labelled "B-PEX" (barrier cross-linked polyethylene) or "barrier PB" (barrier polybutylene). The packaging or the print on the pipe wall states "oxygen barrier" or "barrier pipe." If it doesn't say barrier, it isn't.

Types: PEX vs polybutylene

Both PEX and polybutylene are available as 22mm barrier pipe. They look similar on the shelf but handle differently and have different temperature limits.

For a standard extension with a gas combi boiler, both materials work. The boiler flow temperature rarely exceeds 75°C, well within either rating. PEX's higher temperature tolerance matters if you have a system boiler with a hot water cylinder running at higher temperatures, or as a safety margin if the thermostat overshoots. Polybutylene's flexibility matters if your plumber needs to thread long runs through existing floor joists without cutting notches.

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System compatibility: pick one brand and stick with it

JG Speedfit fittings are designed for JG Speedfit pipe. Hep2O fittings are designed for Hep2O pipe. The outside diameters are identical (22mm), so the pipe physically slides into either brand's fittings. But the internal diameters differ slightly between PEX and polybutylene, which means the pipe inserts (the small plastic stiffener that goes inside the pipe end to stop it collapsing under the O-ring pressure) are not interchangeable.

Using a Speedfit insert in Hep2O pipe, or vice versa, creates a poor seal. The insert may be too loose (allowing the pipe to deform under clamping pressure) or too tight (cracking the pipe wall). Either way, the manufacturer's warranty is void and you've created a potential leak point.

This matters when you're topping up materials mid-job. If your plumber started with Speedfit, don't grab Hep2O pipe from a different merchant because it's in stock. The savings aren't worth the risk.

How to work with it

Cutting

Cut 22mm push-fit pipe with a proper pipe cutter, not a hacksaw. A ratchet pipe cutter makes a clean, square cut every time. A hacksaw leaves burrs on the cut edge, and those burrs damage the EPDM O-ring inside the fitting as the pipe slides past. Damaged O-ring means a slow leak that may not show up during pressure testing but develops over weeks or months as the damaged rubber degrades further.

After cutting, check the end is square. Hold it against a flat surface. If light shows under one side, the cut is angled and the pipe won't seal evenly. Cut again. Deburr the inside and outside edges with a utility knife or fine file, removing any plastic swarf.

Inserting into fittings

Every push-fit pipe has a witness mark printed or etched on the surface, 28mm from the end for 22mm pipe. This mark tells you the minimum insertion depth. When you push the pipe into a fitting, it must pass the witness mark. If it doesn't, the collet hasn't engaged fully and the O-ring isn't seated on a clean section of pipe.

The correct sequence:

1. Cut square and deburr.
2. Push a pipe insert (stiffener) fully into the pipe end. It should sit flush with the cut edge. If it won't go in, the cut is oval and you need to re-cut.
3. Push the pipe into the fitting until the witness mark disappears inside the fitting body. You'll feel a slight click as the collet engages.
4. Pull the pipe back firmly. It should not move. If it slides out, the collet hasn't gripped, most likely because the pipe insert is missing or the pipe wasn't pushed in far enough.

That pull test is not optional. Do it on every single joint. Professional plumbers do it by habit. The five seconds it takes prevents the catastrophic failure that happens when a joint releases under pressure inside a finished wall.

Supporting and clipping

Plastic pipe expands and contracts with temperature more than copper does. A 3m length of PEX on a heating circuit can move several millimetres between cold and hot. Clip it at intervals of approximately 500mm on horizontal runs and 800mm on vertical runs, per manufacturer installation guidance, and allow a slight loop or bend at direction changes so the pipe can move without stressing the fittings. Rigid straight runs clipped tight at both ends and connected to fixed fittings will push against those fittings as they expand, potentially working the collet loose over years of daily heating cycles.

Pressure testing

Before any pipework gets concealed (boarded over, plastered in, screeded), the entire system must be pressure tested. The standard test for push-fit systems is 10 bar for 45 minutes minimum. Your plumber fills the system, pumps it to 10 bar using a manual test pump, and watches the gauge. Any drop means a leak.

Building control may require a pressure test certificate before signing off concealed pipework. Photograph the gauge at the start and end of the test. Keep the photographs with your project records. If a dispute arises later about installation quality, the pressure test evidence is your first line of defence.

How much do you need

For a typical extension plumbing layout, the 22mm pipe runs are relatively short compared to 15mm branches. You're using 22mm for:

• Main flow and return from the boiler to a distribution point (manifold or tee) serving the new radiators: typically 5-15m depending on boiler location.
• Primary hot and cold supply runs from the existing distribution to the new kitchen/utility: typically 3-8m each.
• Bath feed (if the extension includes a bathroom): 2-4m.

A reasonable estimate for a single-storey rear kitchen extension is 15-30m of 22mm pipe. That's five to ten 3m lengths, or a single 25m coil with some left over.

The rule of thumb for sizing: maintain 22mm for the main circuit and distribution runs, then branch down to 15mm for individual radiator connections and single tap feeds. Don't run more than three radiators off a single 15mm branch. If you have four or more radiators on one circuit, keep the main at 22mm and only reduce at each individual radiator tee.

Cost and where to buy

Branded 22mm barrier pipe costs £8 – £12 per 3m length depending on brand and material. Buying a 25m coil brings the per-metre cost down substantially compared to individual 3m lengths. The table below has current pricing from national retailers.

Screwfix and Toolstation carry the widest range. Travis Perkins and Jewson stock Speedfit and Hep2O but prices vary by branch and trade account. If your plumber has a trade account at a builders' merchant, the pipe will likely be cheaper than retail. Ask what brand they're using and whether the price includes barrier pipe specifically, not just "22mm plastic."

Alternatives

22mm copper pipe is the traditional alternative. It's been used in UK plumbing for over 70 years, and the long-term reliability data is overwhelming: a 0.1% failure rate over 20 years compared to 2-3% for push-fit. Copper doesn't need barrier treatment (metal is inherently oxygen-impermeable), doesn't degrade with UV exposure, and is immune to rodent damage. Professional plumbers who work on high-end or insurance-sensitive installations often prefer copper for concealed runs and use push-fit only for accessible connections.

The trade-off is speed and skill. Soldering copper requires a blowtorch, flux, solder, a fire blanket, and the ability to make a clean joint. A plumber working in push-fit can complete a first-fix plumbing layout in roughly half the time. That labour saving is real money on your quote.

A common compromise, particularly popular on forum threads among experienced installers: use copper for the main concealed runs (under floors, inside walls) and push-fit for accessible connections (in airing cupboards, behind bath panels, at manifold points). You get copper's reliability where you can't access a failure, and push-fit's speed where you can.

For the 15mm branch runs off your 22mm main circuit, see the 15mm push-fit pipe page.

Insurance: a risk most guides don't mention

UK water leak claims cost insurers around £2.5 million per day, and push-fit poor workmanship is identified as one of the most common causes. Some home insurers are responding by increasing excesses on water damage claims where push-fit pipework is installed, or by adding exclusions for concealed push-fit joints.

This doesn't mean push-fit is uninsurable. It means installation quality matters, and having evidence of correct installation (pressure test certificates, photographs of pipework before concealment, a named and insured plumber who fitted it) matters when you make a claim. If your plumber installs push-fit throughout and you have no pressure test record, you're exposed.

Check your buildings insurance policy for any exclusions related to plastic pipework or push-fit systems before your plumber starts. Most standard policies don't exclude it. But some do, and discovering that after a leak is not the time to find out.

Common mistakes

Forgetting pipe inserts. Every push-fit joint needs one. They come in the bag with the fittings, they fall on the floor, they get lost in sawdust, and then the pipe goes in without one. The joint looks fine. It passes the pressure test. Three months later, you have a leak behind the skirting board. Check every joint. If you can see the pipe end inside the fitting and there's no silver or white insert visible, the stiffener is missing.

Using non-barrier pipe on heating circuits. The packaging doesn't always make it obvious. If the pipe or the packaging doesn't explicitly say "barrier" or "oxygen barrier," assume it isn't. Non-barrier pipe is cheaper because it's simpler to manufacture. It's fine for cold water supply. It will slowly destroy your heating system.

Mixing brands. Speedfit pipe with Hep2O fittings, or grabbing whatever's in stock at the merchant without checking compatibility. The pipe slides in, the collet grips, and the joint looks identical to a correct one. But the insert doesn't match the pipe ID, and the O-ring seating is compromised. Stick to one brand throughout.

Concealing joints without pressure testing. Once the floorboards go down or the plasterboard goes up, accessing a failed joint means ripping out finished work. Every joint, every time, must be pressure tested before concealment. 10 bar, 45 minutes, no drop.

Not allowing for thermal movement. A 3m run of plastic pipe on a heating circuit expands noticeably between cold and full operating temperature. Clipping it rigid at every point along a straight run forces the expansion stress into the fittings at each end. Leave slight flex in the clips and allow a small loop or offset at direction changes.

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Not photographing before concealment. Building control requires evidence that primary circulation pipework is insulated (Approved Document L). Photographs of your pipework runs with insulation fitted, taken before the floor goes down, satisfy this requirement. They also protect you in an insurance claim. Take them. Store them with your project file.

Where you'll need this

• First-fix plumbing - main flow/return heating runs from the boiler to new radiator circuits, primary hot and cold distribution to the new kitchen

22mm push-fit pipe appears during the first-fix plumbing phase of any extension or renovation that adds radiators or extends the hot water distribution. It's one of the less expensive materials on the job, but getting it wrong (wrong type, poor installation, concealed joints without testing) creates the kind of slow, hidden failure that costs thousands to fix once the build is finished.