Push-Fit Plumbing Fittings: Speedfit, Hep2O & Demounting — When & How

Summary

Push-fit fittings transformed domestic plumbing in the 1990s and early 2000s, making pipe connections quick and (when done correctly) reliable without soldering or specialist tools. The dominant UK brands — John Guest Speedfit, Wavin Hep2O, and Polypipe — all use the same basic mechanism: a stainless steel collet grips the pipe, compressed O-rings provide the seal.

The key variable that catches tradespeople out is the pipe insert requirement. Rigid copper pipe doesn't need inserts — the wall thickness maintains the pipe's round profile under the fitting's compression. Flexible plastic pipe (PB, PEX, PEX-a) can deform, and without an insert, the collet grip is unreliable and the O-ring seals unevenly. Missed inserts are the single most common cause of push-fit leaks.

Beyond domestic plumbing, push-fit fittings are used in central heating systems, underfloor heating manifold connections, and as transition fittings between copper and plastic. Understanding their limitations — particularly around demounting, reuse, and temperature ratings — prevents callbacks.

Key Facts

• Speedfit (John Guest) — yellow collet; compatible with Speedfit pipe and standard copper; inserts required for plastic pipe
• Hep2O (Wavin) — white collet; designed for Hep2O pipe; inserts required for PB/PEX pipe
• Polypipe — similar system; largely interchangeable fittings with above
• Pipe insert (stiffener sleeve) — small plastic insert that goes inside the pipe end before inserting into fitting; maintains pipe roundness under collet compression
• Without insert on plastic pipe — O-ring does not seal evenly; collet can slip; pipe pulls out under pressure or thermal movement
• Copper pipe — insert not required; direct push and lock
• MLCP (multilayer composite pipe) — usually requires its own fittings from the system manufacturer; not interchangeable with PB push-fit
• Temperature limit — standard plastic push-fit rated to 85°C continuous, 95°C intermittent; suitable for domestic hot water and central heating
• Pressure limit — typically 10 bar at 20°C; reduces at higher temperatures (check manufacturer data)
• Demounting tool — each brand has its own demounting tool for collet release; a stiff plastic disc that depresses the collet evenly; free at most trade counters
• Reuse — fittings can be demounted and reused IF the collet teeth are undamaged and O-ring is in good condition and undamaged; replace if in doubt
• WRAS approval — most Speedfit and Hep2O fittings are WRAS approved for potable water; check product for the WRAS mark
• BS 7291 — British Standard for thermoplastic pipes and fittings for hot and cold water
• Pipe supports — plastic push-fit pipe has higher thermal expansion than copper; clip spacing 300mm for 15mm, 400mm for 22mm horizontal runs in hot water

Quick Reference Table

Detailed Guidance

Fitting Selection and Pipe Preparation

Correct fitting selection requires knowing:

1. Pipe material — dictates whether inserts are needed
2. Pipe diameter — 10mm, 15mm, 22mm, 28mm are standard domestic
3. Connection type — elbow, tee, straight coupler, male BSP, female BSP, reducing

Pipe preparation:

1. Cut pipe square — use a pipe cutter or fine-tooth saw with a mitre guide. An angled cut means the O-ring does not seal evenly. Push-fit fittings tolerate less imprecision than compression fittings.
2. De-burr the pipe end inside and out. Sharp edges cut O-rings.
3. For plastic pipe: push the insert fully into the pipe end. It should be flush or slightly recessed. If it protrudes, push harder — it must not stick out or it fouls the fitting bore.
4. Mark the pipe at the depth of insertion with a pen. This lets you verify the pipe went in fully.
5. Push pipe into fitting firmly until it stops. Check your mark — if the pipe is short of full insertion, the collet may not have engaged.

Demounting Push-Fit Fittings

When a fitting needs to be removed:

1. Release pipe pressure if in a live system — isolate and drain.
2. Fit the demounting tool (collet release ring/clip) over the pipe at the fitting. If you don't have the tool, a firm push using a piece of pipe as a sleeve works for one-off operations — wrap tape to protect the fitting.
3. Depress the collet ring firmly and hold it depressed.
4. Pull the pipe directly out of the fitting while maintaining collet depression. Do not twist — twisting damages the collet teeth.
5. Inspect the fitting collet (should show even teeth, no deformation) and O-ring (should be round and undamaged). Replace the fitting if in doubt.

Never demount with pliers on the fitting body — this crushes the collet and the fitting is useless. Always use the correct tool.

Common Mistakes and Failures

Missing insert on plastic pipe: The number one failure. Always check — if a plastic push-fit joint is leaking and there's no insert, the whole joint must be remade. The insert cannot be retrofitted to a made-up joint.

Pipe not pushed in fully: Particularly in tight spaces where you can't see the fitting clearly. Always mark the pipe and check the mark after making the joint. A partially inserted pipe will pull out under pressure or thermal cycling.

Re-using a damaged collet: Collet teeth are sharp and grip by digging into the pipe surface. Once distorted or damaged (by a previous hard removal or use of pliers), the collet will not grip reliably. If in doubt, use a new fitting — they cost pennies versus a callout.

MLCP pipe with push-fit fittings: MLCP (e.g., JG Speedfit MLCP, Pexfit, Uponor) must use dedicated fittings from the system manufacturer. Standard Speedfit fittings for PB pipe will not reliably connect to MLCP because the pipe wall construction and hardness are different. This is a common mistake when extending MLCP systems.

Push-fit on heating systems above 85°C: Standard plastic push-fit is rated to 85°C continuous. In a primary heating circuit where temperatures can briefly exceed this during commissioning, use brass compression fittings or press-fit at connection points near the boiler and any ASHP buffer vessels.

Central Heating Applications

Push-fit is widely used in secondary pipework (after the first connection from boiler flow/return) in central heating systems. Key considerations:

• Oxygen barrier requirement: PB pipe for sealed heating systems should be oxygen-barrier type (Hep2O OxyCheck, Speedfit Oxygen Barrier). Standard PB is gas-permeable — oxygen diffuses through the pipe wall into the heating water, accelerating corrosion of the system.
• System inhibitor: all sealed systems require an inhibitor (e.g., Fernox F1, Sentinel X100). This is a BS 7593 requirement regardless of pipe material.
• Expansion: allow for thermal expansion in long plastic pipe runs. Use expansion loops or slip joints in runs over 5m on hot water circuits.

Transition from Copper to Plastic

Speedfit, Hep2O, and similar brands make transition fittings for copper-to-plastic connections. No insert is needed on the copper side; insert is required on the plastic side. The fittings look identical to standard push-fit but are sized to accept copper OD on one side.

Do not cross-mix male thread sizes: 15mm BSP male does NOT fit a 15mm push-fit bore — they are different standards. Always use a proper copper-to-plastic fitting, not a push-fit combined with a threaded adapter.

Frequently Asked Questions

Can I reuse a push-fit fitting?

Yes, if the collet and O-ring are undamaged. Inspect after every removal. The manufacturer's guidance varies — some say fittings can be demounted and reused up to three times; beyond that, replace. In practice, if a fitting shows any collet distortion or O-ring groove contamination, replace it.

Are push-fit fittings as reliable as solder or compression?

When correctly installed (including inserts), push-fit fittings have a good track record. Failures are almost always due to installation errors (missing insert, incomplete insertion, using wrong fittings for pipe type). Compression fittings offer a mechanical advantage — the ferrule bites into the pipe — but overtightening is also a common failure mode. For accessible locations, push-fit is convenient; for concealed pipework in walls or under floors, compression or solder joints are preferred because they are more tolerant of long-term vibration and thermal cycling.

Do push-fit fittings need to be accessible?

BS 7671 for electrical does not apply here, but Water Supply Regulations require that connections to the water supply system should be accessible for inspection. In practice, plumbing joints concealed in solid walls or under floor screeds should use soldered joints or approved concealed-location push-fit fittings (some Speedfit fittings are rated for embedding in screed). Check the manufacturer's approval before concealing any joint.

Regulations & Standards

• BS 7291-1 and -2 — Thermoplastic pipes for hot and cold water: general requirements and PB pipe specifications

• Water Supply (Water Fittings) Regulations 1999 — WRAS approval requirements; accessible connections in water supplies

• BS 7593 — Treatment of water in domestic heating systems; inhibitor requirement

• WRAS (Water Regulations Advisory Scheme) — Approval marking required on fittings for potable water

• John Guest Speedfit Technical Data — Installation guides and temperature/pressure ratings

• Wavin Hep2O Technical Guidance — Fitting specifications and installation

• Water Regulations Advisory Scheme — WRAS approved products search

• BS 7291 British Standard — Thermoplastic plumbing pipe standards

• compression fittings — When compression is preferred over push-fit

• pipe materials — PB, PEX, MLCP, copper comparison

• pipe compatibility — Interchangeability between brands and pipe types

• underfloor heating — Push-fit use in UFH systems, oxygen barrier requirements