Step-by-step installation of a plastic Hepworth manifold

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Step-by-step installation of a Hepworth plastic manifold

The plastic manifold is the heart of every modern branched heating or plumbing system. If installed correctly, it will operate quietly, reliably and without problems for decades. If installed incorrectly, you will have trouble with it – it will drip, air up, one circuit will heat and the other will not, your spouse will turn the thermostat in vain. In this article, I will take you through the entire process of installing a Hepworth plastic manifold from the first measurement through tightening the last nut to bleeding the system. I will not skip anything, because over the years of practice I have seen mistakes at every conceivable place.

This article assumes that you have already chosen a specific type of manifold. If you are still hesitating about the number of circuits, diameter or whether to go for an open or closed variant, first see our articles How to choose a plastic manifold: number of circuits, diameter and type of connection and Open vs. closed manifold – what is the difference and when to use which. Here we go directly to the installation.

What you will need before starting the work

Successful installation does not start with a wrench in your hand, but with plans and a material list on the table. Underestimating preparation is the most common mistake of non-professionals – and then you have to go to the hardware store twice.

Tools

Torque wrench or combination wrench in sizes 24 mm, 27 mm and 32 mm (according to the connection diameter)
Flat and cross screwdriver (mounting the bracket on the wall)
Hammer drill with a concrete drill ø 8 mm (for the wall) or ø 5 mm (for drywall with anchors)
Water level (at least 60 cm long – a smaller one is inaccurate)
Tape measure and pencil
Plastic container or bucket (to catch residual water during the pressure test)
Teflon sealing tape (PTFE) width 19 mm or hemp sealing with paste
Hose for bleeding (diameter according to the bleed valve outlet)

Materials and components

Selected Hepworth manifold (e.g. 4-circuit with valve 15 × 15 × 15 × 15 for four separate circuits or 3-circuit closed 22 × 15 for a three-circuit system with a common 22 mm connection)
3/4" manifold bracket – without it, the manifold hangs in the air and the hose connections carry the entire mechanical load
Appropriate anchors and screws for the wall (usually M6 × 50 or M8 × 60 according to the system weight)
Hose clamps or compression fittings (depending on the type of pipe you use)
Sealing rings / O-rings (always have a few spare ones, sometimes they are missing or damaged when unpacked)
Valve grease or Teflon for threaded connections

Step 1: Selection and preparation of the installation location

The manifold must be placed in such a way that it is easily accessible – not built behind a tile, not behind a washing machine, not behind a boiler without any space. You will need to access it for bleeding, possible flow change or service work. The minimum free space in front of the manifold is 40 cm, ideally 60 cm.

Choose the installation height so that the circuit outlets are clearly visible and accessible. In the installation in a distribution box, it is guided by the position of the box. In a free installation on the wall, the common height of the center of the manifold is 120–150 cm from the floor – this is an ergonomic height for working with the valves.

Check that the wall can support the load. A fully filled three-circuit manifold with pipes and water can weigh up to 8–12 kg. A concrete or brick wall is ideal. In drywall, you must hit the profile or use special drywall anchors (Molly-bolt) with a load capacity of at least 15 kg each.

Marking the position of the bracket

Place the 3/4" manifold bracket on the wall and use the water level to align it horizontally. A deviation greater than 2 mm in 30 cm will cause the manifold to be sloped – air will accumulate at one end and bleeding will be difficult. Mark both screw holes with a pencil.

Drill the holes with a hammer drill. For concrete or masonry, use a drill bit ø 8 mm and anchor S8, for drywall use Molly anchors ø 10 mm. Tighten the screws firmly, but without excessive torque – the plastic bracket withstands compression worse than metal.

Step 2: Mounting the bracket and installing the distributor

The bracket is mounted, the wall has drilled holes, and the screws are tightly tightened. Now, slide the distributor into the bracket. Plastic Hepworth distributors have two locking protrusions or grooves on the body that fit into the bracket hooks. The procedure is simple: place the distributor from below under the bracket hooks and with a slight upward movement, secure it. You should hear a soft click or at least feel that the body is firmly seated.

Check whether the distributor is not tilted. Even if the bracket is horizontal, the distributor may be installed with a slight deviation. Looking from the side, confirm that it is in the same plane as the wall. If it wobbles or "sways", check whether the bracket hooks are fully secured and whether the protrusions on the distributor are not damaged (this can happen due to improper storage in the cold – the plastic becomes brittle).

Step 3: Preparing threaded connections

This is the step where the tightness of the system for the next few years is decided. Threaded connections on plastic Hepworth distributors are either external or internal G 3/4" thread (or G 1/2" on 15 mm loop outlets). Plastic is not steel – it must not be over-tightened.

Sealing selection: PTFE vs. hemp

I recommend using PTFE (Teflon) tape exclusively for plastic threads. Hemp sealing with paste is more mechanically aggressive and the paste can attack certain types of plastics – the manufacturer Hepworth explicitly does not recommend it. PTFE tape is wound in the direction of the thread (clockwise when viewed at the end of the thread), 3–5 layers are sufficient. Too many layers will make threading difficult and can cause the thread to crack when tightened.

When connecting fittings where one side is metal and the other is plastic, always wind the tape on the metal thread (external). If you are winding on a plastic external thread, be careful – wind it without tension, just by gently pressing the tape against it.

Tightening plastic threads – torque and feeling

Golden rule: after reaching mechanical resistance (you can no longer screw it further by hand), tighten with a wrench by an additional 1/4 turn – maximum 1/2 turn. No more. Plastic does not have the same elasticity as steel and over-tightening will cause the thread to crack – usually a longitudinal crack that is not visible but causes a leak.

If you have a torque wrench, for a G 3/4" thread on polypropylene use a torque of 25–30 Nm, for G 1/2" a maximum of 20 Nm. These values are conservative, but safe for full-body plastic Hepworth distributors.

Step 4: Connecting the supply and return pipes

A plastic distributor always has one main inlet and one main outlet (for the supply and return of the common loop). The remaining openings are the outlets for individual branches. The connection order is logical:

First, connect the main supply and return – that is, the larger pipe (22 mm or 28 mm). Working with larger pipes is mechanically more demanding, and if you start with the loops, you risk loosening or damaging the smaller connections while working.
Then connect the individual loops – 15 mm outlets (or 12 mm for smaller systems). Connect each loop one by one, from one end of the distributor to the other. For example, with a 4-loop distributor 15 × 15 × 15 × 15, start with loop 1 (the outermost), then continue with 2, 3, 4.
Finally, check all connections visually and with a gentle twist without a wrench – the connection should not move and should be firmly seated.

Pay attention to the flow direction. Most Hepworth distributors are symmetrical, but some types (especially those with integrated valves or check valves) have a flow arrow on the body. Ignoring this detail will cause the check valve to block the flow – the system will be filled, but no flow will occur.

For systems with two loops, a 2-loop closed 22 × 15 is suitable (if you want to have a closing option on both branches without an additional valve) or a 2-loop open 22 × 15 (if you have ventilation/regulation solved elsewhere in the system). The difference between open and closed versions is explained in detail in the article Open vs. closed distributor – what is the difference and when to use which.

Step 5: Filling the system and pressure test

Before filling, close all outlet loops (rotary valves or ball valves at the ends of the loops). Open the main supply only partially – not fully. Reason: fast flow lifts dirt from the system and it can settle in the valves or in the distributor itself.

Water filling procedure for the heating system:

Open the filling valve (usually at the boiler) by about 1/4 turn.
Watch the pressure gauge – the pressure should slowly rise. The normal operating pressure for a closed heating system is 1.2–1.5 bar when cold.
When the pressure reaches 1.0 bar, close the filling valve and inspect all joints with a flashlight. Look for any drops, damp areas or whiteness (dried water = a leak that has stopped).
If everything is dry, continue filling to the operating pressure.
Finally, perform a pressure test: pressurize the system to 1.5 times the operating pressure (i.e. 1.8–2.2 bar) and let it stand for 30 minutes. A pressure drop of more than 0.1 bar indicates a leak.

A pressure test is a legal requirement for new installations in many cases (depending on the scope of work). Either way, it is also your protection – if the customer calls in a month saying their heating is leaking, and you have a pressure test protocol, you are covered.

Step 6: Bleeding all circuits

Air in the system is the main enemy of manifold systems. It manifests as noises (bubbling, knocking), uneven heating (one circuit heats, the other does not) and a gradual drop in system pressure. Bleeding must be done thoroughly and in the correct order.

Bleeding procedure

Start the circulation pump (if you have one) at minimum speed – air moves better at low flow.
Start at the highest point of the system – air rises, so the bleed valve at the top is first in line. If your manifold has an integrated bleed valve on top, use it first.
Proceed circuit by circuit: open the first circuit, at the end of the circuit (at the radiator or at the highest point) bleed the radiator valve. Wait until no more air is coming out and water starts to drip. Close the bleed valve.
Move to the next circuit. Repeat the procedure.
After bleeding all circuits, check the pressure – it usually drops slightly during bleeding. Re-pressurize to 1.2–1.5 bar.
After 24 hours, bleed again – air is released from water gradually and after the first filling, there is always more air than it seems.

Step 7: Setting the flow in individual circuits

This is a step that most installers skip and the customer then "treats" for years. If you have a manifold with control valves (e.g. 4-circuit with valve 15 × 15 × 15 × 15), each circuit must be hydraulically balanced.

Hydraulic balancing means that each circuit receives exactly the amount of water it needs based on its thermal output and length. A long circuit (e.g. 80 m of floor heating) has a higher hydraulic resistance than a short circuit (e.g. 20 m). Without balancing, the short circuit will be overfilled and the long one underfilled.

Practical balancing procedure for a household without measuring instruments:

Let the system run for at least 30 minutes at full load (boiler at maximum, all circuits open).
Measure the temperature of the supply and return pipes at each circuit with your hand or a laser thermometer. The difference between supply and return should be roughly the same for all circuits (typically 10–15 °C for radiator systems).
The circuit with a smaller difference (e.g. only 5 °C) is overfilled – water is flowing too fast and not delivering enough heat. Slightly close the valve.
The circuit with a larger difference (e.g. 20–25 °C) is underfilled – water is flowing too slowly and overcooling. Slightly open the valve.
Repeat the measurement after 20 minutes and adjust. Ideally, do five to seven iterations.

Common installation errors – what I have seen in practice

Over the years of field work, I have encountered hundreds of installations, both good and bad. Here is a selection of the most common errors to watch out for during your own installation:

Installation without a bracket – a manifold hung only on hoses. Hose connections are not designed for mechanical load. After a year of vibrations and thermal expansion, the joints will loosen.
Over-tightened threads – see above. A plastic thread cracked during installation will leak only after a year, when the crack has "grown" due to heat and pressure cycles. The customer calls, but you don't know why.
Input and output mixed up – especially with closed manifolds with a check valve. The system can be filled, but the pump won't circulate.
No bleeding performed – the customer calls after a week saying "the heating doesn't work". It doesn't work because there is an air pocket the size of a fist in circuit 3.
Missing gasket between adapter and manifold – the O-ring fell out of the package, the installer didn't notice, the system leaks a drop per hour, the customer notices only after two months, when the wall under the manifold is wet.
Wrong diameter – e.g. a 22 mm manifold connected to a 28 mm main pipe with a reduction without balancing. The flow is limited and the system never reaches the designed performance. More about this issue in the article What manifold diameter do I need: 15 mm, 22 mm or larger?
Water manifold instead of a heating manifold – a topic in itself, we dedicate a whole article to it Water manifold vs. heating manifold – can I use the same one?

Special situations: installation in a distribution box

If you are installing a manifold into a prefabricated distribution box (usually in floor heating), the procedure is slightly different. The box usually has its own mounting for the carrier – there is no need to drill into the wall. It is important to:

Check that the internal dimensions of the box match the dimensions of the manifold (including space for valves, actuators and possible flow meters).
Leave space for the supply and return pipes at the bottom/top of the box – usually 10–15 cm.
Keep in mind that the box will be built into the wall or recess. After closing, the lid must be accessible for maintenance. The box doors MUST NOT catch on actuators, flow meters or wiring.
The manifold's air vent must point upwards and be accessible after opening the box doors.

Maintenance after installation – what and when to check

The plastic manifold Hepworth is a low-maintenance component. If installed correctly, it does not require regular maintenance in the true sense of the word. I still recommend the following regular tasks:

Once a year (best at the beginning of the heating season): visual inspection of all connections – no moisture, white coating (dried lime deposits = old leak), corrosion on metal parts.
Once a year: check the pressure in the system. A pressure drop of more than 0.2 bar during the heating season without a visible leak may indicate a micro-leak in the manifold or elsewhere in the system.
After each heating season: bleed the system even if you think it is unnecessary. Air is continuously released from the water, especially in the first 2–3 years after filling a new system.
Every 5 years: check the condition of O-rings and seals on detachable connections. Plastic O-rings age and harden – a cracked seal is only a matter of time before it starts to leak.

For more information on maintenance and inspections, read our separate article Maintenance and inspection of plastic manifolds – what and how often to check.

Most frequently asked questions (FAQ)

Do I have to turn off the entire heating system when installing a plastic manifold Hepworth?

Yes, always. Working on a pressurized and heated system is dangerous. Before installation, turn off the boiler, let the system cool down to a temperature below 40 °C and drain the relevant section of the system. If you are working on a completely new installation (the manifold has not yet been connected), it is not necessary to deal with the boiler, but ensure the shut-off valves on the main supply are closed.

Can I use sealing paste (e.g. Loctite 577) instead of PTFE tape on the plastic thread?

This is not recommended and the manufacturer of Hepworth manifolds does not allow it. Anaerobic sealants (Loctite and similar) are primarily intended for metal threads and their chemical reaction can damage plastic – polypropylene and PE. An exception are special sealing pastes certified for use with plastics, but even these are not commonly used where PTFE tape is sufficient.

How many circuits can one manifold handle and how do I know if the system is oversized?

The number of circuits depends on the specific model (2, 3, 4 and more). Oversizing the manifold (too many circuits with low flow in each) is indicated by insufficient heating – each circuit receives too little water. Undersizing (too few circuits with overloaded branches) causes noise and uneven heat distribution. We cover this in detail in the article 2-circuit vs. 3-circuit vs. 4-circuit manifold – which one suits my system.

Can a leak occur if the manifold is properly installed but not bled carefully enough?

Yes. Sudden opening of the bleed valve at full system pressure (1.5 bar and more) can cause a hydraulic shock inside the manifold body. In plastic components, this can lead to micro-cracks in the material, which may result in a leak after several thermal cycles. Always open the bleed valve slowly, only 1–2 turns, not all the way.

Is it normal for a new plastic manifold Hepworth to slightly steam or leave a water mark on the surface after the first filling?

Mild condensation on the surface of the plastic body is normal – the plastic is colder than the surrounding air when filled with cold water and humidity from the air condenses. If the condensation disappears within 30–60 minutes, it is not a leak. If the wet mark remains or increases, it is a real leak and you should check all threaded connections according to the procedure in step 3.

What to do if during the test run one circuit flows and the other does not at all?

First suspicion: air lock. Bleed the non-functional circuit directly at its highest point. Second suspicion: forgotten closed valve – check whether the circuit valve is in the open position (ball valve parallel to the pipe = open). Third suspicion: kinked circuit pipe – during installation, a kink or knot in the pipe circuit can block the flow. This is a common problem in floor heating, where pipes are laid into concrete mortar.

Conclusion

Installing a plastic manifold Hepworth is not rocket science, but it is a job where every detail counts. Correct placement and securing of the carrier, responsible preparation of the threads, gradual filling, thorough bleeding and finally hydraulic balancing – these are the steps that distinguish an installation the customer will forget about for years from an installation they will return to every season. If you invest time into each step correctly, the Hepworth manifold will repay you with decades of reliable operation without worries.

If you have not yet selected a specific manifold, browse the full range of plastic manifolds Hepworth in our category and use other articles in the Knowledge Centre – for example Common problems with plastic manifolds: leaks, air in circuits and weak flow or Frequently asked questions about plastic manifolds Hepworth.

Do you have a question about this topic?

Not sure what to choose or dealing with a specific situation in your home? Write to us – we are happy to help.