MLCP multilayer pipe for plumbing and heating: a practical guide

MLCP has become a common choice for radiator circuits, manifold primaries and water runs because it comes in long coils, needs no flame and needs fewer fittings than copper. It also has its own rules on sizing, bending and joining that catch out installers used to copper.

This guide covers sizes and bores against copper, where MLCP can and can't go, how to join and bend it, how much it expands, and what the Water Regulations say about hidden pipe. For comparing pipe for the underfloor loops themselves, see UFH pipe types compared.

What is MLCP pipe?

MLCP is a layered pipe: an inner plastic pipe, a thin aluminium tube, and an outer plastic layer, bonded together with adhesive layers. The plastic is usually PEX (PEX-AL-PEX) or PE-RT (PERT-AL-PERT).

• It holds a bend. The aluminium stops the pipe springing back, so runs stay where you put them.
• It is oxygen-tight. The aluminium layer stops oxygen getting into the heating water, which protects the pump, manifold and heat source.
• It expands little. One maker's data gives a linear expansion of 0.024mm per metre per °C.
• It is light and comes in coils. MaxHeatUFH stocks 16mm PERT-AL-PERT in coils up to 500m, and PEX-AL-PEX from 20 to 32mm on 50m coils.

What size MLCP replaces 15mm, 22mm and 28mm copper?

Match the bore, not the outside size. MLCP sizes are the outside diameter, and its walls are thicker than copper, so the same number gives a smaller bore.

Typical UK copper tube is 15 x 0.7mm (13.6mm bore), 22 x 0.9mm (20.2mm bore) and 28 x 0.9mm (26.2mm bore). So:

• Use 16mm MLCP for short radiator tails and UFH loops, where 15mm copper would be used.
• Use 20mm MLCP for longer 15mm runs, or where you want a little more flow.
• Use 25mm MLCP in place of 22mm copper, and 32mm in place of 28mm.

Size the pipe from the heat load and flow rate, as you would with copper. Don't simply swap 22mm copper for 20mm MLCP, as the bore drops from about 20mm to 16mm.

Where can I use MLCP?

MLCP suits most wet heating and water pipework inside the building. It is not for gas, and it should be kept out of direct sunlight.

On drinking water, the pipe and fittings must both be suitable under the Water Fittings Regulations. MaxHeatUFH MLCP fittings are rated for hot and cold water. Our multilayer pipe listings are for underfloor heating and heating, so email sales@maxheatufh.com before using them on a drinking water supply.

Temperature is the other limit. One maker rates its multilayer pipe at 10 bar, with 70°C working for underfloor heating and 90°C working for radiators. MaxHeatUFH MLCP press fittings are rated 10 bar and 80°C continuous, so design the system to run at or below 80°C.

How do you join MLCP pipe?

Press fittings are the standard joint, with compression fittings for repairs and adaptors where MLCP meets copper.

The MaxHeatUFH MLCP press fittings have a brass body, a stainless steel press sleeve with an inspection window, and factory-fitted EPDM O-rings. To make a joint:

1. Cut the pipe square with a pipe cutter.
2. Calibrate and bevel the bore with a reaming tool or chamfering tool, so the pipe is round and the O-rings aren't cut.
3. Push the pipe fully home until it shows in the inspection window.
4. Press with the U-profile jaw that matches the pipe size.

A press-to-copper tail has a plain copper-sized end that goes into a 15, 22 or 28mm copper fitting. The size is written MLCP first, so 20mm x 22mm joins 20mm MLCP to 22mm copper. For which jaw goes on which tool, see M-profile vs U-profile press jaws.

How tight can I bend MLCP?

One maker gives a minimum bending radius of 5 times the outside diameter without a bending spring. Bending instead of fitting an elbow saves money and keeps the flow smooth.

An external bending spring supports the outside of the pipe so it doesn't kink. For repeated, neat bends on 16 to 32mm pipe, the MLCP manual pipe bender (£95) bends up to 90 degrees with a former for each size. Where there is no room to bend, use an elbow. Check your pipe maker's figures, as they vary.

How much does MLCP expand, and how should I fix it?

Using 0.024mm per metre per °C, a 10m run that warms from 10°C to 70°C grows by 10 x 60 x 0.024 = 14.4mm. That is small, but it has to go somewhere.

• Leave room for movement at bends and changes of direction, rather than clamping a long straight run tight at both ends.
• Use the pipe maker's clip spacing for exposed runs, and clip close to each side of a fitting.
• Straighten coiled pipe for exposed runs. The pipe straightener (£137) takes the coil set out of 16 and 20mm pipe for neat manifold and radiator connections.
• Insulate flow and return runs in unheated spaces. Pre-insulated PEX-AL-PEX comes in red for flow and blue for return.

Can MLCP be buried in a wall or floor?

For heating and underfloor heating loops, yes, as part of a designed system that has been pressure tested before it is covered. On a water supply, the Water Fittings Regulations are stricter. Schedule 2, paragraph 7 says no water fitting shall be embedded in any wall or solid floor, and limits which fittings can be concealed. A concealed fitting includes one enclosed in a chase or duct, or in any position that is inaccessible or makes access difficult.

MLCP helps here, because long coils let you run unbroken lengths through floors and walls with no joints along the way. Run water pipes in a sleeve or duct so they can be withdrawn, and keep joints where you can reach them. Our guide to press, solder and compression fittings explains the concealed joint rules in more detail.

Worked example: a 6 radiator circuit in MLCP

A small extension with 6 radiators, 20mm flow and return mains (2 x 20m) and 16mm tails (6 x 2 x 3m). Prices inc VAT, October 2026.

• PEX-AL-PEX 20mm, 50m coil for the mains: £58
• PERT-AL-PERT 16mm, 50m coil for the tails: £37
• 12 chrome radiator elbows, 16mm x 15mm, 150mm pipe at £6: £72
• Manual pressing clamp tool set, 16 to 32mm U profile: £90
• Pipe cutter £7, 16mm chamfering tool £8, 20/25/32mm chamfering tool £4.23

That is £167 in pipe and radiator elbows and £109.23 in tools, before the tees, ball valves and press-to-copper tails, which are sold by the bag. Size the mains from the heat load: on larger systems, 25mm mains may be needed.

Products for this job

• PEX-AL-PEX multilayer pipe, 20 to 32mm: from £58
• PERT-AL-PERT multilayer pipe: from £37
• Pre-insulated PEX-AL-PEX pipe: from £111
• MLCP press fit to copper brass tail: from £9 a bag
• MLCP press radiator elbow 16mm x 15mm: from £6
• 16mm MLCP compression coupling: £3.55
• MLCP manual pipe bender 16 to 32mm: £95
• All MLCP fittings

Related guides: M-profile vs U-profile press jaws, UFH pipe types compared and Connecting a UFH manifold.

Frequently asked questions

Is MLCP better than copper for central heating?

It is faster to install, needs no flame, bends by hand and comes in long coils with fewer joints. Copper is rigid and handles higher temperatures, and some appliance instructions set rules for the pipe at the connections. Many systems use both, joined with press-to-copper tails.

What size MLCP do I need instead of 15mm copper?

16mm MLCP has a 12mm bore, smaller than 15mm copper's 13.6mm, so it suits short tails. For longer runs, 20mm MLCP (16mm bore) gives more flow than 15mm copper.

Can I connect MLCP to copper pipe?

Yes. Use an MLCP press fit to copper brass tail, which has a copper-sized end for a 15, 22 or 28mm compression, solder or press fitting. For 16mm to 15mm with spanners only, use a compression adaptor.

Does MLCP need an oxygen barrier?

No separate barrier is needed. The aluminium layer is the oxygen barrier, which is one reason MLCP is used on heating systems.

Can I join MLCP without a press tool?

Yes, with compression fittings made for multilayer pipe, such as the MaxHeatUFH 16mm MLCP compression coupling and elbow. They suit repairs and accessible joints. For a low-cost press option, the manual clamp set (£90) presses 16 to 32mm without power.

What pressure and temperature can MLCP fittings take?

MaxHeatUFH MLCP press fittings are rated to a maximum working pressure of 10 bar and 80°C continuous, with a 95°C peak.

Can MLCP be left exposed?

Indoors, yes, clipped neatly and straightened. Outdoors or anywhere in direct sunlight, protect it, as makers advise keeping multilayer pipe out of direct sun.

Sources: Giacomini multilayer pipe technical data (R999), Water Supply (Water Fittings) Regulations 1999, Schedule 2