Most Common Mistakes in HEPWORTH Installation

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The HEPWORTH system is one of the popular plastic pipe systems for heating and hot/cold water distribution - installers praise it mainly for its speed of work and low weight compared to copper or steel. However, this apparent simplicity is also the reason why installation mistakes are made that only show up months later - a dripping joint in the wall, a cracked elbow the first time the system heats up, or unevenly warm radiators in the house. In this article we have collected the mistakes that installation companies most often encounter with the HEPWORTH system, including how to easily avoid them and which components are worth keeping in the van for every installation.

There is no need to worry - the vast majority of these mistakes have nothing to do with the complexity of the system itself. It is more about routine, haste, or underestimating a detail that is forgiven more easily with other materials. Let's go through them in order, from pipe fixing all the way to the final pressure test.

Mistake No. 1: Incorrect spacing and type of pipe supports

The most common mistake we see when checking complaints is trivial - the pipe is fixed too infrequently or with the wrong clamps. Plastic pipe has significantly higher thermal expansion than metal and lower inherent stiffness, so if the gap between supports is too large, the pipe will sag over time, air collects at the point of sag, and unwanted "waviness" appears in horizontal sections, visible to the naked eye even after being covered with plasterboard.

In practice, a simple rule applies - the larger the pipe diameter, the larger the support spacing that can be used, but never arbitrarily large. For common diameters used in family houses, installation companies have found the following approximate maximum spacings for horizontal runs to work well in practice: 16 mm - approximately 50 cm, 20 mm - approximately 60 cm, 25 mm - approximately 70 cm, and 32 mm - approximately 90 cm. For vertical runs (risers), the spacing can be slightly extended, because the pipe is not stressed by the weight of its contents in the same way as in horizontal runs, but even there it is not worth experimenting and exceeding the spacing by more than 20%.

The second half of this mistake relates to the type of fixing. For plastic pipe it is worth using clips with a soft insert or at least a sufficiently wide contact surface, which does not pinch the pipe and at the same time allows it slight longitudinal movement during thermal expansion. A metal clip with a sharp edge, tightened too tightly, is one of the most common reasons why a microcrack appears exactly at the fixing point after a few years of operation - the pipe cannot "breathe" freely at that point and all the stress concentrates right there.

If you are dealing with fixing a larger number of parallel pipe runs at once - for example in a plant room or when leading to a manifold - it is worth considering machine-applied pipe fixing using clips joined into a strip, applied directly with a suitable tool, which significantly speeds up installation compared to manual screwing of individual clamps one by one. It is precisely for larger installations, where dozens of metres of pipe need to be fixed at regular intervals, that we have found HS 45mm clips for machine pipe fixing, joined by wire into a strip useful - they are supplied in a strip, so they can be applied quickly one after another at a constant spacing, which is exactly what you need for the "waviness" problem mentioned above.

HS 45mm clips for machine pipe fixing, joined by wire into a strip - ensure even support spacing without manual measuring at each clip, ideal for longer straight sections leading to the manifold. Price from 21.77 EUR.

Mistake No. 2: Poorly tightened or poorly prepared compression joints

The second group of mistakes, which we see in practically every other complaint caused by leaks, relates to joining pipes using compression fittings. This type of joint is very practical on one hand - it does not need welding or a pressing tool, and can be disassembled and reassembled - but it is exactly this simplicity that leads many installers to underestimate the preparation.

We most often encounter these three variants of the same mistake:

Uneven or angled pipe cut. If the pipe is not cut exactly perpendicular to its axis, the sealing ring will not seat evenly around the whole circumference at the joint, and the joint will leak exactly at the point where the cut is most angled. The cut should be made with suitable plastic pipe shears, never with a metal hacksaw without subsequent deburring.
Missing or insufficient edge chamfering. After cutting, the pipe edge needs to be slightly chamfered (faceted), otherwise the sealing ring or clamp can be scratched or pushed out of position when inserted into the compression nut, which outwardly shows up as a joint that holds at first but starts leaking microscopically after a few weeks.
Incorrect tightening torque. This is paradoxically a mistake that works in both directions. A too loosely tightened joint logically leaks. But overtightening "by force" without a torque wrench is equally problematic - with a plastic or softer metal compression joint body, this can cause a micro-crack in the thread or deformation of the sealing ring, which only shows up after several temperature cycles, when the material loses its original elasticity.

The recommended procedure, which has proven itself in practice and which we also recommend following when training new installers, is as follows - always in the same order, without skipping steps:

If you are installing a transition from plastic to copper pipework, for example when connecting to an older radiator or boiler with a copper connection, it is important to use a compression fitting designed directly for copper pipe in the correct diameter - combining mismatched diameters "by force" is another classic source of leaks. For the common 15 mm copper pipe diameter, Compression fitting for copper pipe - 15x1-EK has proven itself in practice, as it has a sealing geometry adapted exactly to this copper diameter, so there is no need for any additional sealing with hemp or Teflon tape (which, incidentally, is another common mistake - additional Teflon taping of a compression joint that is designed to seal metal-to-metal or with a ring only complicates proper seating there).

Compression fitting for copper pipe - 15x1-EK - correctly sized transition when connecting a HEPWORTH run to existing copper pipe, no need for additional Teflon taping. Price from 2.51 EUR.

Mistake No. 3: Omitting or incorrectly placing the sludge trap filter

The third very widespread mistake does not concern the pipe itself, but the overall system concept - installation without a mechanical sludge (dirt) filter, or placing it in the wrong location. Even though HEPWORTH pipe is inherently clean and does not corrode like steel pipework, small impurities still get into the system during installation anyway - cutting shavings, sealant residue, construction dust - and when the circulation pump is first started up, all of this flows exactly to the most sensitive points: thermostatic valves, the manifold, and the circulation pump itself.

In practice, this looks like the system working without problems for the first few weeks, but after a few months minor leaks start appearing at thermostatic heads, or the pump starts "buzzing" and losing performance - this is a typical sign that dirt has settled somewhere in the circuit that should have been caught by a filter that was never installed there.

The sludge trap filter should therefore be installed right at the system inlet, before the manifold, ideally at a point with good access for regular cleaning (once a year; for new installations we recommend the first check after just three months of operation). Cyclonic sludge trap filters also use a centrifugal principle, so the captured particles do not significantly increase the system's pressure loss the way ordinary mesh filters do once clogged.

For larger installations, where the entire supply needs to be filtered before splitting into individual circuits, we have found the Cyclonic sludge trap filter 4" - 1/2"F useful - in operation we have noticed that even after a year of normal operation in a family house it captures a surprisingly large amount of small impurities that would otherwise end up directly in the thermostatic valves on the radiators.

Cyclonic sludge trap filter 4" - 1/2"F - protects the manifold, pump and thermostatic valves from installation debris, the centrifugal principle reduces the risk of clogging. Price from 102.34 EUR.

Mistake No. 4: Incorrect balancing and connection of the manifold

If the system supplies several circuits at once - for example several radiator branches, or a combination of radiators and underfloor heating - the manifold plays a key role. Here we see two typical mistakes that overlap with each other.

The first is physically connecting the supply and return the wrong way round, i.e. "crossed". With some manifolds the system can cope with this without a major problem (circulation simply works in the opposite direction to what was originally intended), but with manifolds that have a built-in flow meter or a thermostatic head on one of the sides, this causes the control to simply not work as it should - the head throttles flow in the return instead of the supply, which confuses the whole logic of temperature control.

The second, much more widespread mistake is completely omitting the balancing of individual circuits after connection. With a 4-circuit manifold, where each branch has a different length and a different number of radiators, each circuit needs a different flow rate for all rooms to be heated evenly. If the valves on the manifold are not adjusted (for example, if all circuits are left "fully open"), the nearest and shortest branch will "steal" most of the flow and the most distant room stays cold - this is exactly the classic scenario where a customer complains that "one room is always cold", while the boiler and the pump are working perfectly fine.

When building a new manifold, or when replacing an old piecemeal solution with one compact unit, the 4-circuit manifold with valve, 15 x 15 x 15 x 15 has proven very useful in practice - it has its own shut-off valves on each branch straight from the factory, so balancing the individual circuits is a matter of a few minutes' work with an installation wrench, not buying separate control elements on top.

4-circuit manifold with valve, 15 x 15 x 15 x 15 - its own shut-off valves on each branch make it easy to correctly balance flow between circuits of different lengths. Price from 41.69 EUR.

Mistake No. 5: Incorrect orientation of thermostatic control valves

The fifth mistake, which is repeated especially among less experienced installation companies, is reversing the direction of flow when installing a straight radiator thermostatic control valve. Most of these valves have an arrow stamped on the body showing the direction the water should flow when correctly installed - and this arrow is not just a formality. The internal design of a straight thermostatic control valve is designed so that the control cone throttles flow precisely in this direction; if the valve is installed the wrong way round, control either does not work predictably at all, or the head throttles flow "backwards", which outwardly shows up as a radiator that either does not react at all to changes in the head setting, or reacts with a significant delay.

The second, related mistake is swapping the order of the valve (supply) and the shut-off fitting (return) - i.e. fitting the thermostatic control valve on the return instead of the supply. With some types of radiators this is not visible immediately, because the radiator still heats up anyway, but temperature control stops being precise, because the thermostatic element reacts to the temperature of the return water instead of the temperature of the water entering the radiator.

When choosing a specific valve, we recommend always checking whether it is a straight or an angled variant (depending on how the pipework runs to the radiator in a given room) - using the wrong type forces the installer to "bend" the pipe right next to the valve, which increases stress in the joint exactly where you need it least. A proven part for straight pipe runs to a radiator is, for example, the Straight thermostatic radiator control valve, EK x 1/2", which connects directly to plastic pipe via a compression end fitting (EK), so there is no need for an additional transition piece.

Straight thermostatic radiator control valve, EK x 1/2" - direct connection to plastic pipe via a compression end fitting EK, when installing remember to follow the flow direction according to the arrow on the valve body. Price from 8.58 EUR.

Mistake No. 6: Forgotten pipe dilatation

The sixth, and perhaps most underestimated, mistake is completely ignoring the thermal expansion of plastic pipe on longer straight sections, especially when routed in the floor or in a shaft alongside a riser. Plastic pipe expands significantly more with temperature change than metal - and if a long straight section is cast permanently into a concrete screed or fixed at both ends without any play, the only place the expansion can "hide" is the pipe body itself or the nearest joint.

In practice this looks like fine cracking sounds appearing after a few heating seasons when the heating starts up (a typical "clicking" sound in the wall or floor as the pipe shifts), or in an extreme case the joint at the point where the pipe is most fixed gets damaged. The solution for longer straight sections is either to leave a compensation loop (the pipe "waves" slightly in plan view, giving it room to expand), or to use sliding (not fixed) fixing along part of the route, where one point serves as the fixed point and the remaining supports allow the pipe free longitudinal movement.

This is exactly why we emphasised the type of clamp in the first chapter of this article - a clip with a soft insert, which does not pinch the pipe, also functions as a sliding point for dilatation. If a metal clip tightened "to the max" is used instead at every single fixing point, dilatation simply has no room, and the whole problem just moves elsewhere - most often to the nearest joint or elbow.

Mistake No. 7: Omitted or premature pressure test

The seventh, and in terms of consequences the most serious, mistake is omitting the pressure test before covering the pipework - that is, before casting it into the floor, plastering over a chase in the wall, or closing a suspended ceiling. This mistake is not made out of bad intent, but out of time pressure - there is a schedule on the construction site, another trade is already waiting to take over the space, and a pressure test that would take "a few hours longer" is sometimes simply skipped with the reasoning that "well, it looks fine".

The problem is that the vast majority of mistakes described above - a poor edge chamfer, an insufficiently tightened compression joint, missing dilatation - may not show up at all under normal operating pressure and room temperature. They only show up during the first significant temperature cycle (heating switched on in autumn) or after a few months, when the sealing ring "settles" slightly. If the pipe is already cast into the floor by that point, the repair means breaking out the screed instead of a few minutes tightening a nut.

The recommended procedure is to carry out a pressure test at a minimum of 1.5 times the system's operating pressure, for the duration specified by the project documentation or local practice (typically several hours with continuous monitoring of pressure drop), and always before even a single metre of pipe is covered. Visual inspection of all joints during this test is just as important as the pressure measurement itself - microscopic moisture around a compression joint is often visible before it shows up on the pressure gauge.

Mistake No. 8: Incorrect slopes and missing venting

The last, eighth mistake we will mention in this overview relates to air in the system. Plastic pipe is often routed along the shortest possible path between points A and B during installation, which is fine in itself, but if the route contains local "humps" - places where the pipe rises briefly and then drops again - air collects exactly at the highest point of such a section, and cannot easily be pushed out from there towards the vent valve on the radiator or manifold.

The result is gurgling in the pipes, reduced performance of a particular radiator despite the valve being correctly open, and repeated complaints that "that same radiator needs venting over and over again". The solution is to take care already at the pipe route design stage that horizontal sections rise slightly towards the nearest venting point, and to avoid unnecessary local dips just to get around an obstacle, if the obstacle can be avoided some other way (for example by changing the routing height along the whole run, not just at one point).

For this reason it is also an advantage with manifolds if the manifold has its own automatic, or at least manual, vent valve directly at the highest point of its body - the same applies to the 4-circuit manifold mentioned above, where it is enough to open the vent on the manifold when first filling the system, before the system starts filling towards the individual circuits.

How to check these mistakes before handing over the work

To summarise the whole procedure into a practical checklist, before handing over any HEPWORTH installation to the customer (or before covering the pipework), it is worth going through the following points - in this order, not randomly:

The experience of installation companies we spoke to while preparing this article shows that the individual mistakes are not responsible for complaints to an equal degree - the most problems are caused by missing dilatation and insufficiently tightened or prepared compression joints, i.e. exactly the mistakes that do not show up right after installation is finished, but only after the first real temperature cycle or after a few months of operation.

The 28% figure for dilatation is not random - this mistake is the most treacherous precisely because the system behaves completely problem-free for the first year, and neither the installer nor the customer have any reason to doubt the quality of the installation. The problem only appears after repeated temperature cycles, when the material "fatigues" a spot that had no room to move - and by that point hardly anyone remembers that the cause was a lack of play at the pipe fixing from a year or two earlier.

Frequently Asked Questions

Can HEPWORTH pipe be cast directly into a concrete screed without a protective conduit?

In most cases it is recommended to run the pipe in a protective conduit, which, besides mechanical protection, also leaves the pipe room for the thermal expansion described above in the dilatation section. Direct casting without any play increases the risk that stress from expansion is transferred directly to the nearest joint.

How often does the sludge trap filter need to be cleaned after installation?

For a new installation we recommend the first check after approximately three months of operation, since that is when leftover installation debris is still being "cleaned out" of the system. For a settled-in system, an annual check is then usually enough, ideally before the start of the heating season.

Why is one radiator still colder than the others, even though the valve is fully open?

The most common cause is an unbalanced manifold - nearer or shorter circuits "steal" flow from more distant branches, as described in the manifold balancing section above. The second possible cause is air trapped in a local dip in the pipe route leading to that radiator.

Does the pressure test have to be recorded in writing, or is it enough that it was carried out?

We recommend always producing at least a simple written record (date, test pressure, duration, result) and attaching it to the handover documentation for the work. In the event of a complaint, such a record is the only proof that the test took place before the pipework was covered.

Can a compression joint still be tightened further after years of operation if it starts leaking slightly?

Yes, that is one of the main advantages of compression fittings over welded or pressed joints - the joint can be gently tightened even after years of operation, as long as it is accessible. However, if the leak is caused by a damaged sealing ring or a clamp scratched during installation, tightening alone will not solve the problem and the sealing elements need to be replaced.

Is a special tool needed to chamfer the pipe edge before a compression joint?

For common diameters used in family houses, a simple manual chamfering tool or even a fine file is sufficient; the important thing is to make the chamfer evenly around the whole circumference. For serial installation of a larger number of joints, it is worth investing in a combined tool that cuts and chamfers in one step, which also reduces the risk of an uneven cut mentioned in the first chapter of this article.

Have a question on this topic?

Are you dealing with a specific problem installing the HEPWORTH system, or not sure which component you need? Write to us - we're happy to help.