Metallic Pipe

MLCP Frequently Asked Questions (FAQs)

Q. Do I need special training to install Uponor MLC (Multilayer composite)?
YES. MLC is extremely easy to install, but we always recommend that all installers undertake the free, on-site certificated training offered by Uponor

Q. Do I need special tooling to install MLC?
YES. There are several different connection methods for use with the MLC system. Most of these need specialist tooling of some sort which would be demonstrated in the free training offered by Uponor. For the press type connections, specialist hydraulic tooling is required. These can be purchased from Uponor or can also be hired from several national hire companies such as BSS Hire It, TG Lynes and Broughton Plant Hire

Q. When pressing connections on Uponor MLC, what jaws do I need?
There are many jaw profiles in the marketplace, but ONLY jaws supplied by Uponor are permitted for use on our press fittings. No other manufacturer’s jaws can be used on Uponor press systems.

Q. I already have a press tool for use on metal press systems, can I use this on Uponor MLC?
There are many tools available for making joints on various press connection systems. Uponor do have a list of approved hydraulic press tooling that can be used in combination with the Uponor jaws. No other tools can be used other than the approved tools. Please contact Uponor for advice on the approved hydraulic press tools

Q. Can I use MLC for a continuously operated re-circulating system?

YES. As Uponor MLC is manufactured to EN ISO 21003, it is permitted to be used for a DHW recirculating system.

Q. Will Uponor MLC be affected if I bury the pipe in a screed?
NO. Uponor S-Press PLUS press fittings use high grade materials that are no affected by the chemicals found within a standard screed. However, all other fittings other than Uponor press fittings, should be protected if being buried in a screed.

Building regulations require that any pipes laid for domestic services are able to be withdrawn from a screed in case of a product failure. For this reason, MLC pipe-in-conduit may need to be used to lay a pipe in the screed.

Q. Can I use MLC as a discharge pipe from a boiler or cylinder safety valve?
NO. Discharge pipework should be capable of temperatures that exceed the maximum working temperature of the MLC system. For this reason we recommend that an all metal system is used for these types of safety discharge outlets.


Q. Does MLC require insulating?
YES. MLC should be insulated to suit the Building Regulations. All insulation should comply to the relevant national standards (BS 5422) to prevent heat loss or transfer of heat

Q. Are Uponor MLC fittings colour coded?
Uponor metal press fittings and the Uponor RS riser system fittings are all colour coded for easy identification. In fact, even the MLC pipes have colour coded end plugs for easy size identification. To help select the correct jaw for each fitting, even these are colour coded for easy size identification.

Q. What is the maximum working pressure for MLC?
The maximum operating pressure for MLC is 10 bar for all building services

Q. What is the lowest temperature water MLC can carry?
With the addition of a suitable Glycol based antifreeze mixed with the water in the pipe, Uponor MLC can carry water at temperatures as low as -20°C

Q. Do I need to use a special type of sealant on the MLC threaded fittings?
NO. However, we advise using a sealant approved for use with the application that the installation is intended for (i.e potable water). Details of the correct methods of installation should be sought from Uponor

Q. Can Uponor MLC be used for a solar thermal type installation?
There are two parts to a solar thermal installation, the primary side (which circulates water around the solar panels) and the secondary side. As the water in the primary side can reach temperatures above the maximum operating temperature of MLC, we do not allow MLC to be used on the primary side of the installation. However, once the heat has been passed though a cylinder to the water in the secondary side of the system, MLC is suitable provided all the necessary protective thermostatic controls are used on both the primary and secondary sides of the installation, and the working temperature does not exceed the maximum operating temperature specified by Uponor

Q. Can I use MLC to carry oil?
NO. Prolonged exposure to fuel oils can damage the MLC system

Q. Can I use MLC to convey gas?
NO. The Uponor MLC system is NOT designed or certificated for gas in the UK

Q. Can I use MLC for compressed air systems?
NO. Uponor MLC it is not recommended for this type of system

Q. Can direct sunlight or UV light damage MLC?
YES. As with virtually all plastics, sunlight and UV light will degrade the material if they remain exposed for prolonged periods. Exposed pipework should always be protected from direct sunlight or UV

Q. Can I bury MLC underground?

No. Without protection, the MLC pipe could be damaged or crushed. Uponor supply a special range of pipes called Ecoflex that are designed for underground use. We recommend the use of Ecoflex systems for all applications where the pipe is to be buried in the ground

Q. Can I place MLC pipe into gypsum plaster structures?
YES. This will have no detrimental effect on the pipe.

Q. Can I use MLC pipes outside, i.e. under decking?
NO. This is not really recommended. Without adequate protection the pipe would be susceptible to accidental damage, frost, sunlight, etc.

Q. Can I apply silicone sealant onto MLC pipe?
NO. Most sealants have an active ingredient which keeps the sealant from solidifying or curing. Some of these chemicals may cause damage to the pipe material

Q. Can I use MLC on a condensate drain from a condensing boiler?
NO. We do not recommend MLC for this application

Q. Can I run de-ionised water through MLC pipe?
YES. it is perfectly safe to use MLC for this application.

Q. Can I use MLC in hard water areas?

YES. The smooth bore of MLC prohibits the build-up of limescale inside the pipe.

Q. Can I use MLC in soft water areas?
DEFRA and the Water Authorities set standards for the maximum acidity of water. Using Uponor MLC to connect to a water supply from one of the recognised licenced Water Authorities will have no detrimental effect on the system. However, care should be taken when connecting to a private supply water source as these supplies can be outside of the Government controlled water quality conditions and may cause damage to the MLC system. If you are connecting to a private water supply, we advise you submit a water report to Uponor to check compatibility with the MLC materials

Q. Can I use any lubricant on MLC fittings?
NO. MLC fittings do not need to be lubricated. Some lubricants can damage the MLC system, will invalidate the guarantee and may contravene the necessary hygiene standards

Q. Does condensation form on MLC pipe as it can do on copper pipes?
When being used with cold water or chilled water applications, condensation may form on the surface of the pipe, but to a significantly lesser amount than a copper or stainless steel pipe. However, as an MLC pipe does not suffer from corrosion, the condensation will not affect the MLC pipe material


Q. Can MLC pipe be used for Underfloor Heating?
YES. This is a standard practice and Uponor can offer expert advice on the installation of underfloor heating systems

Q. Can MLC pipe & fittings be used on a power shower?
YES. MLC is absolutely fine for this type of application

Q. Is MLC suitable for use on a solid fuel heat sources such as wood burning boilers or biomass heat sources?
There are generally two parts to a wood burner or solid fuel heat source installation, the primary side (which circulates water from the burner to a buffer tank) and the secondary side which uses the energy stored in the buffer tank. As the water in the primary side can reach temperatures above the maximum operating temperature of MLC, we do not allow MLC to be used on the primary side of the installation. However, once the heat has been passed through a cylinder to the water in the secondary side of the system, MLC is suitable provided all the necessary protective thermostatic controls are used on both the primary and secondary sides of the installation, and as long as the working temperature does not exceed the maximum operating temperature specified by Uponor


Q. Can I use a corrosion inhibitor in my MLC system?
YES. An MLC system will not corrode and does not specifically require an inhibitor in it’s system. However, other metal parts of a heating system will need the help of an inhibitor to prevent corrosion and damage. Products similar to Fernox F1 and Sentinel X100 will not damage MLC as long as they are used correctly. Any commercial water treatments that are used in the MLC system should be either approved by Uponor or be underwritten by the engineer applying the treatment to the system.

Q. Does chlorine have an adverse effect on MLC pipe?
Chlorination of a drinking water system is a common practice in modern buildings. However, these treatments can stress ALL materials in a drinking water system and disinfection treatments should be kept to a minimum in order to give the maximum longevity to the life of ALL the materials within a system. Constant or very repetitive chlorination can damage materials within a syatem. Any chemicals added to a system must only be done by a qualified professional that follows all the correct safety procedures and should be competent with both the chemicals being used and the system they are treating.

Q. Can I install an Electronic Limescale Remover on MLC pipework?
YES. Electronic or magnetic equipment to reduce the build-up of limescale elsewhere in the system will not affect a MLC system.

Q. How far away should I position MLC pipe from down-lighting?
Fire regulations state this must be positioned a minimum of 150mm from the down-lighting fitting. The pipe should also be protected from strong light emitting from the down-lighting.

Q. Can I use expanding foam to seal around MLC?
NO. Chemicals in the foam, in particular before it cures, can damage the MLC pipe. We recommend providing a sleeve around the pipe to which the foam can be applied without affecting the pipe inside.

Q. My system requires a high flow rate. How will this affect MLC?
The design of the MLC system and the materials used are not affected by high volume flow rates, and will not suffer from either erosion corrosion or unacceptable water noises that will normally affect metal pipe systems. Seek advice from Uponor if you have specific requirements for high water velocities

Q. Can I use Denso tape on MLC pipe?

NO. Many adhesive tapes can use chemical adhesives that can affect the MLC pipe materials. If in doubt, please seek advice from Uponor

Q. How do I connect MLC to a radiator TRV?
Most threads on a TRV are ½” BSP type. In this case, you can use a compression adapter to connect the MLC pipe straight to the TRV valve. Part numbers 1013813, 1048100 or 1013806 depending on the pipe size being used.

Q. Are there any other ways to connect to a radiator from MLC?
There are several other ways to connect to a radiator from MLC, such as radiator connection elbows, or radiator upstands. We recommend that you discuss options with our Technical Team

Q. Can I put MLC through a hole in a wall?

YES. Wherever there is a potential for damage due to expansion or movement, we recommend that the MLC is protected when going through the wall by using a protective sleeve

Q. Can I plaster over MLC piping in a wall?
YES. Standard plaster will not have any effect on the pipe material, although we recommend the pipes are buried deep enough not to crack the plaster surface if the pipes expand and move

Q. How do I connect MLC to an incoming blue MDPE service pipe?
Ideally the external MDPE pipe should terminate at an approved isolation valve inside the building and the MLC can then be connected to the other side of the valve with either an MLC compression adapter fitting, or a male/female threaded adapter.

Q. Can I use MLC as a discharge from a macerator (e.g. Saniflo)?
NO. This is not recommended.

Q. What happens if I kink MLC pipe?
As the MLC has a metal layer in its composition, this should be avoided. However, pipes are extremely robust and a kink in the pipe may have virtually no effect on the capability of the pipe until a repair has been made. If in doubt, seek advice from Uponor.

Q. Is it possible to trace heat MLC pipe?

YES. Trace heating can be applied, but must never be stuck to the pipe using any form of solvated adhesive, and also must be thermostatically controlled to prevent temperatures in excess of 55°C. Seek advice from Uponor’s Technical Team

Q. How can I trace the pipes within a stud wall or under a wooden floor?
NHBC guidance state that pipes should be traceable when placed within a wall or under a floor void. Uponor MLC has a metal layer in its composition, this layer will make the system traceable when using a stud detector piece of equipment.

Q. To make an alteration to my system whilst it is still filled, can I freeze MLC pipe?
YES. Care must be taken when freezing any pipes and should only be done by an experienced engineer.

Q. How do I pressure test my system once I have installed it?
Pressure testing must only be carried out by a competent trained engineer. Details of Uponor’s latest suggested testing procedure should be sought from Uponor’s Technical Team

Q. Is there a transition connection to join MLC to other materials?
Yes. Uponor supply connections to connect to metal press systems, copper compression fittings and Uponor MLC. BSP threaded adapters, flanges and copper tail adapters can be used to connect to all other types of pipe system

Q. Can I pressure test MLC using air?
YES. However, because air is a compressible medium and pressure testing with high pressure air can be dangerous if not done properly, any testing using air must only be done by a competent trained engineer. Testing using air must be done at very low pressures and over a much longer time period than testing with water. Details of Uponor’s latest suggested testing procedure should be sought from Uponor’s Technical Team.

Q. Is it possible to blank off an MLC pipe to allow testing of the system?
Uponor can supply a range of reusable test plugs that can be used with sizes from 14 – 40mm. In addition Uponor supply a press connection ‘stop-end’ for sizes 16 – 32mm or an RTM ‘stop-end’ to close of 16mm pipe ends

Q. How do I control the thermal expansion of the MLC pipe?

As a guideline, Uponor MLC will expand slightly more than an equivalent copper pipe. Methods of controlling this expansion are identical to a copper system and must be designed into the plumbing scheme. Please seek advice from Uponor’s Technical Team for expansion control methods

Q. Is there a minimum radius which MLC pipe can be bent?

YES. There are minimum bending radii for each size of pipe. These radii vary depending on whether the bend is being made using a bending spring, by an approved bending tool or just simply being bent by hand. Please refer to Uponor for the correct suggested bending radii

If you have any other questions other than the above, please contact our Uponor Technical Team on 01923 927015