Joining and Sealing HEPWORTH Pipework

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Why Joining and Sealing HEPWORTH Pipework Is Key to a Trouble-Free Heating System

Most complaints about heating systems that installation companies and DIYers run into don't originate in the boiler, the pump, or the radiators themselves. Most often it's something far more mundane - a leaking pipe joint. A drop of water on a garage ceiling, a damp patch on plasterboard under underfloor heating, or a cloudy pressure gauge after a pressure test - these are all signs that a joint wasn't made correctly, or that the wrong sealing material was used. This is just as true for the HEPWORTH system as for any other pipework, perhaps even more so, since several joint types are often combined on one run - from compression fittings through press joints to threaded fitting connections.

This article is a practical guide showing which joint types are actually used with HEPWORTH pipe, which sealing materials make sense and which are just a leftover habit from when things were made a bit differently, what tightening torque is optimal, how to test a joint, and what to do when a joint still leaks despite everything. The goal isn't to sell you as many parts as possible, but to show you how to make a joint once, properly - because reworking pipe that's been built into a wall or cast in screed is always more expensive and more unpleasant than a few extra minutes during installation.

What joint types are used with HEPWORTH pipe

Before we get into sealing materials, it's worth being clear on what mechanical joint types are actually encountered in practice on this pipework. Each has its place, its advantages and its weaknesses, and the choice isn't just a matter of price, but also of where the joint will be (visible pipe in the boiler room, a cast floor, a shaft) and who will do the installation.

Compression fittings

This is the most widespread type of detachable joint for both copper and plastic pipe of smaller diameters. The principle is simple - a union nut and a compression ring are slid onto the pipe, the pipe is inserted into the fitting body, and tightening the nut compresses the ring around the pipe, creating both a seal and a mechanical joint. The advantage is that the joint can be taken apart at any time without damaging either the pipe or the fitting, which you'll appreciate especially during servicing or when replacing valves or manifolds. The downside is greater sensitivity to correct tightening torque - an undertightened joint leaks, an overtightened one can damage the compression ring or even deform the pipe.

A typical example is the compression fitting for copper pipe 15×1-EK, commonly used exactly on pipework to radiators, manifolds and fittings in the boiler room.

Press joints

With press joints, a fitting with an embedded O-ring is slid onto the pipe and pressed with special pliers - the deformation creates a permanent, non-detachable joint. The advantage is installation speed (one press takes a couple of seconds) and high reliability, provided the correct press jaws are used for the given diameter and system. The downside is that the joint can no longer be taken apart - if there's a mistake, the section of pipe has to be cut out and replaced with a new one. Press joints are therefore recommended mainly for runs that won't be opened up again once cast or built in, while detachable compression fittings belong more in visible, serviceable spots like the boiler room or a manifold cabinet.

Threaded joints with a sealing material

The third type is classic threaded joints, where tightness isn't achieved by deforming metal, but by a sealing material right in the thread - PTFE tape, hemp with sealing paste, or, for flat joints, a rubber seal or O-ring. This joint type is used mainly for connecting fittings, valves, pumps and manifolds, where two elements with a standard internal or external thread need to be connected (for example 1/2", 3/4" or 1"). An example is connecting the thermostatic radiator valve - straight, EK x 1/2", which connects on one side via a compression fitting to copper or plastic pipe, and on the other side via a 1/2" thread directly into the radiator.

For a quick idea of how time-consuming each joint type is in typical installation practice, see the following overview. The figures are based on one installer's typical working pace on pipe up to 28 mm diameter, and include preparation, the joining itself, and a visual check (for a solvent-welded joint, also the time needed for the adhesive to set before it's put under pressure).

Sealing materials - what actually works

The joint type itself is only half the battle. The other half is choosing and correctly applying the sealing material. This is exactly where most mistakes happen, because many installers (even experienced ones) use the material they're used to, regardless of whether it's actually suitable for the given joint.

PTFE tape

PTFE tape is the most common sealing material for smaller threaded joints, especially with plastic fittings and fine-threaded fixtures. It's applied in the direction of screwing (so it doesn't unwind while tightening) in three to five layers, with the first thread usually left bare - this prevents the tape from being pushed into the pipe and possibly contaminating the system with shreds of tape. The advantage of PTFE tape is clean, fast work; the downside is lower resistance to large temperature swings with repeated disassembly of the joint - after the third or fourth disassembly, it's recommended to apply fresh tape rather than reuse the old.

Hemp with sealing paste

For larger threads (3/4", 1" and up), typically on manifold, pump-group, or larger fitting connections, the classic combination of hemp fibre and sealing paste still proves its worth. The hemp is wound in the direction of the thread and the paste both lubricates during tightening and seals microscopic irregularities in the thread. This combination has the advantage that even if the joint loosens slightly (for example from vibration during circulation pump operation), it keeps its seal longer than tape alone. The downside is messier work and the need to always have fresh, non-dried-out paste.

O-rings and rubber seals

Where a joint isn't secured by a thread but by compression (for example precisely with compression fittings or manifold flange joints), an O-ring or a flat rubber seal takes over the sealing function. The key here is to check that the ring sits exactly in its groove, isn't twisted or pinched, and isn't damaged by a nick or ageing (loss of elasticity, cracks). Old, hardened O-rings are exactly one of the most common causes of leaks when reassembling already-used fittings - so it's worth having spare seals on hand every time an older joint is disassembled.

The following diagram summarises the process of making a typical compression joint, from preparing the pipe to the final check - this process applies practically the same way to both copper and plastic pipe with compression fittings.

Step by step - installing a compression fitting on copper pipe

For a clearer picture, let's spell out the procedure more specifically for the most common case - connecting 15 mm copper pipe with a compression fitting to a radiator valve or manifold.

Cut the pipe square - ideally with a pipe cutter, not a hacksaw. An angled or wavy cut is one of the most common reasons the compression ring doesn't seat evenly and the joint leaks at the very first pressure test.
Deburr the edge both inside and outside - a sharp or burred edge can damage the sealing ring during insertion.
Slide on the union nut and compression ring in the correct order and orientation - the ring usually has a slightly conical shape, and which side faces the fitting body matters.
Push the pipe in fully into the fitting body, and check that it sits straight and isn't skewed.
Hand-tighten the nut as far as it will go, then tighten further with a wrench by the prescribed angle or torque (more in the next section).
Carry out a pressure test before insulating or covering the joint.

When working in the boiler room or on a manifold cabinet, it's worth having good-quality compression fittings with proven ring geometry on hand - poor-quality, overly soft rings can weld together or crack under ordinary tightening.

Compression fitting - for copper pipe 15x1-EK - exactly the type of joint you'll use to connect 15 mm copper pipe to a radiator valve, manifold or fitting in the boiler room, with no need for press pliers. From €2.51.

Tightening torque and force - how much is enough, and when is it too much

One of the most common questions installers ask is: "How hard should I tighten this?" The answer isn't "as much as possible" - an overtightened joint can deform the compression ring, damage the thread, or even squeeze the pipe itself enough to narrow the flow cross-section at the joint. Conversely, an undertightened joint is the most common cause of a slow, hard-to-spot leak that only shows up after weeks of operation as a damp patch.

In typical installation practice, these approximate torque values are recommended for compression fittings on copper pipe (this applies to good-quality brass fittings; for plastic systems, always follow the fitting manufacturer's values):

15 mm pipe - approx. 15 Nm
22 mm pipe - approx. 25 Nm
28 mm pipe - approx. 35 Nm

In practice, without a torque wrench, a simpler rule applies - hand-tighten as far as it goes, then tighten further with a wrench by roughly three-quarters to one full turn, depending on the diameter. If in doubt, it's always better to slightly tighten a joint after the pressure test than to overtighten it from the start.

How to test a joint - the pressure test

No joint may be insulated, built into a wall, or cast into screed without a pressure test. Common practice is to pressurise the system to 1.5 times operating pressure, for at least 30 minutes, with the pressure drop not exceeding about 0.1 bar. For a typical home heating system with an operating pressure around 2 bar, that means a test pressure of roughly 3 bar; for systems with an operating pressure of 4 bar (typical for taller buildings or systems with a height difference), the test is done at 6 bar.

During the test, it's important to go through all the joints visually - especially the ones in harder-to-reach spots, at wall penetrations, or under a manifold. It's a good idea to have a dry cloth or paper towel on hand and gently wipe each joint with it - a damp mark is revealed this way much sooner than waiting for a visible drip.

For underfloor heating or pipework that will be cast into screed, it's worth documenting the test with photos showing the pressure gauge and a timestamp - in the event of a future complaint, this is the only proof the joints were sound before casting.

The most common causes of leaks and how to avoid them

From installation companies' and service technicians' long-term experience, the causes of joint leaks can be roughly broken down as follows: an insufficiently tightened joint accounts for about 45% of cases, a damaged or aged seal (O-ring, rubber seal) about 25%, an incorrectly chosen or incorrectly applied thread sealant about 20%, and the remaining 10% is mechanical damage to the pipe itself (scratches, dents from an unsuitable mount, frost-damaged pipe).

This breakdown leads to a practical conclusion - if you suspect a leaking joint, the first step isn't immediate disassembly and replacing the seal, but a simple check and a bit more tightening. Only when tightening doesn't help does it make sense to take the joint apart and check the condition of the sealing ring or tape. That's exactly why it's worth always having spare O-rings and new compression fittings on hand during servicing - swapping a cheap part right away saves a repeat visit.

Protecting joints from debris and mechanical stress

A leaking joint doesn't necessarily arise from an installation mistake - even a well-made joint can fail over time if it's exposed to excessive mechanical stress (the pipe expands and contracts slightly with temperature during operation, and if it isn't properly mounted, this stress transfers to the nearest joint) or if mechanical debris gets into the system and gradually damages the sealing surfaces in valves and fittings.

The first measure is correct and sufficiently frequent mounting of the pipe along its whole route, so no section hangs freely and overloads joints during thermal expansion. The second, often underestimated measure is filtering the inlet water, especially if the system is fed from a public mains supply or a well with a higher content of mechanical debris - sand and sediment gradually wear down even good-quality seals in valves and manifolds.

HS clips 45mm for machine-assisted pipe mounting - correct, regular pipe mounting along the whole route reduces mechanical stress on joints from thermal expansion and extends their lifespan. From €21.77.

Cyclonic sediment filter 4" - 1/2"F - captures mechanical debris before it reaches valves and manifolds, protecting sealing surfaces from premature wear. From €102.34.

Joining at manifolds and multi-circuit systems

Joints at manifolds deserve their own section, since several circuits, and therefore several joints, meet in one place at once. The risk of a mistake is higher here simply because several joints need to be made and checked in a short time, and it's precisely with repetitive, routine work that one of the joints most often gets "forgotten" during the final tightening.

A proven approach is to work through the manifold circuit by circuit during installation - always finish one joint including its visual check before moving to the next, rather than loosely connecting all circuits first and tightening them all at the end. When pressure-testing a manifold with four or more circuits, it's worth having a second person available to check the joints on the far side of the manifold while the first watches the pressure gauge.

4-circuit water manifold with valve, 15x15x15x15 - a typical example of a spot where several joints meet at once, so it's worth working circuit by circuit and checking each joint right away. From €41.69.

Connecting fittings and valves - where mistakes happen most

When connecting radiator valves, thermostatic heads and similar fittings, a compression fitting on the pipe side is usually combined with a threaded connection on the radiator or valve body side. The most common mistake here isn't the compression fitting itself, but exactly the threaded connection to the body - either PTFE tape is forgotten (wrongly relying on "metal on metal seals anyway"), or the tape is wound in the opposite direction to the screwing, so it unwinds during tightening and the joint leaks despite the effort.

Thermostatic radiator valve - straight, EK x 1/2" - combines a compression fitting on the pipe side with a 1/2" threaded connection to the radiator, so it needs attention on both joint types at once. From €8.58.

Practical tips from installation practice

To finish, a few small but field-tested pieces of advice worth keeping in mind for every installation:

Never tighten a compression fitting "by feel" the first time you work with a new type of fitting - if you have no experience with the specific manufacturer, check the torque or use a torque wrench instead.
After the first pressure test and a short period of operation (a few days), it's worth visually checking the joints once more - slight settling of a seal is normal, and it's sometimes worth gently tightening the joint a bit more.
Never combine an old, already-used seal with a new fitting just because "it still looks fine" - the cost of a new O-ring or compression fitting is negligible compared with the risk of a repeat service call-out.
When working in enclosed spaces (shafts, suspended ceilings), always leave access to at least one joint along the run for any future check, even if the rest of the pipe is permanently pressed.
Mark the date and type of sealing material right at the joint or in the installation log - this will save you time on a future service call deciding exactly what needs replacing.

Frequently asked questions

How often does a compression fitting need retightening after years of operation?

With a correctly made and tested joint, it generally doesn't need retightening at all - a good-quality compression ring keeps its seal long-term. If a slight leak appears after a long period of operation, gently tightening it by a fraction of a turn is usually enough. If that doesn't help, it's better to check the condition of the compression ring rather than keep forcing it tighter.

Can PTFE tape be replaced with a liquid sealant in a spray or tube?

Liquid sealing products have their place, but for threaded joints on heating pipework, classic PTFE tape or hemp with paste is still recommended in practice - they have proven long-term stability under temperature changes. Only use a liquid sealant where the manufacturer of the specific fitting explicitly recommends it.

Can I combine a compression fitting from one manufacturer with a fitting from another?

At the same diameter and thread type, it's usually possible, but it's not without risk - compression ring geometry varies slightly between manufacturers and might not fit exactly into another manufacturer's fitting body. If possible, use the union nut, ring, and fitting body from the same manufacturer, especially for important or hard-to-reach joints.

What do I do if a joint still leaks after repeated tightening?

If tightening to the recommended torque doesn't help, the problem usually isn't the tightening force but a damaged sealing ring, an uneven pipe cut, or a damaged thread. In that case it's always better to fully disassemble the joint, check all the components, and, if in doubt, replace both the compression fitting and the sealing ring with new ones, rather than continue forcing it tighter.

Is a pressure test needed even for a small repair of a single joint?

Yes - even when repairing a single joint, it's worth carrying out at least a short pressure test before insulating or covering the spot again. The cost of a mistake that only shows up after covering is always higher than the extra few minutes spent checking.

Which joint type is most suitable for underfloor heating under screed?

For spots that will be cast and inaccessible after installation, non-detachable press joints with a proven O-ring are clearly recommended, never compression fittings nor threaded joints sealed with tape or hemp - those belong in visible, serviceable spots like a manifold cabinet or the boiler room.

Have a question about joining or sealing pipework?

Not sure how to handle a specific joint in your boiler room, or unsure what sealing material to use? Write to us - we're happy to help.