PRESS Fittings with External Thread - How to Properly Connect to a Radiator

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Press-through fittings with external thread are essential components when connecting crimped ALPEX pipe to standard radiator valves or fittings, where it is necessary to bridge different connection systems. Their correct installation ensures tightness and long-term heating functionality without the need for complex cutting or welding work. This article focuses on practical steps and technical details that distinguish a professionally executed threaded transition from a common mistake.

Choosing the correct type of transition according to the connector

When selecting a transition, it is crucial to first determine the exact size of your crimped pipe and the subsequent thread on the radiator, as the wrong type leads to the impossibility of installation or water leakage. In the range you will find specific models such as press-through fitting - external thread - 1/2"Mx16, which is intended for thinner pipe with a diameter of 16 mm and a standard half-inch thread on the radiator.

However, it is often more important to choose between variants for 20 mm and 26 mm pipe, since most domestic heating systems work precisely with these dimensions. For 20 mm pipe, use model press-through fitting - external thread - 3/4"Mx20, while for the more robust 26 mm pipe, the version press-through fitting - external thread - 3/4"Mx26 is used.

Determine the exact outer diameter of your plastic pipe before purchase.
Check the thread on the radiator valve to see if it is 1/2" or 3/4".
Look at the depth of entry into the radiator to choose a sufficiently long transition.

The key role of the O-ring and surface preparation

The tightness of the entire connection is not only dependent on the mechanical compression by the crimping tool, but primarily on the integrity of the rubber O-ring, which is part of each quality fitting. If the ring is damaged, dry or incorrectly placed, crimping will have only a temporary effect and water will start to leak already during the first pressure test. Therefore, it is necessary to always use the original O-ring - for PRESS fittings brass - 26x3 or equivalent for the given size, never use disassembled parts again.

Before actually placing the transition on the pipe, it is necessary to thoroughly clean the end of the ALPEX pipe from stains, grease and dust, which could damage the sealing surface of the rubber ring. Use a clean cloth and, if necessary, a slightly damp cloth, but never use solvents that can aggressively affect the rubber and cause it to age quickly.

Check that the inside of the transition is free of foreign bodies and that the O-ring is exactly in the groove, not turned or twisted. An incorrectly placed ring can shift out of its original position during crimping, thus completely losing its function.

Crimping procedure and quality check of the joint

Crimping of the transition with an external thread is carried out in the same way as with any other crimped joint, with the critical point being to maintain the exact insertion length of the pipe into the fitting. Each manufacturer specifies an exact value in the technical sheet, which you must measure from the edge of the pipe to the edge of the crimping zone; if the pipe is inserted too little, a gap will form, if too much, the rubber ring may deform. Proper crimping includes placing the crimping pliers on the marked zone and applying full pressure until the pliers themselves release the crimped part.

Quality control of the crimped joint should be immediate and visual – the crimped zone must have a regular hexagonal shape without visible cracks or material deformations. The tool should automatically "click" and release after the process is completed, indicating that the required pressure has been achieved. Never attempt to push or re-crimp the same point, as this permanently damages the metal and cancels the seal.

If you have doubts about the quality of the crimping, you can use the measurement of the distance between the edges of the hexagon, but for normal practice it is sufficient to check whether the crimping tool has performed its function correctly. After checking the external appearance, it is also advisable to check the inner side to see if any foreign body has entered the sealing.

Mounting on the radiator and wall mounting

When the transition is securely crimped onto the pipe, it is followed by its connection to the radiator valve, which requires caution when tightening the threaded joint. When tightening, use two wrenches – one to fix the crimped body so that the entire pipe does not rotate and is not pulled out of the crimp, and the other to tighten the radiator valve nut. Over-tightening can damage the thread on the radiator or tear the sealing material, while insufficient tightening causes water leakage.

For the stability of the entire structure, it is advisable to use a mounting template for attaching the wall panels, which will help keep the radiator in the correct position and prevent the threaded connections from being overloaded by the weight of the radiator. A template such as mounting template - for attaching wall panels PRESS - 100-150mm allows precise setting of the height and distance, which is crucial for the aesthetic result and the functionality of the system.

Fix the body of the transition with one wrench to prevent the pressed joint from loosening.
Tighten the radiator valve with the second wrench to the recommended torque.
Use the mounting template for stable attachment of the radiator to the wall.
Test the tightness of the joint before closing the walls.

Common installation errors and their solutions

One of the most common errors is the use of an incorrect length of transition, which leads to the thread being either too deep in the radiator or, conversely, protruding so much that the valve cannot be properly mounted. Another common problematic situation is improper positioning of the pipe before pressing, when the pipe is bent or twisted, causing uneven pressure distribution during pressing and subsequent cracking of the sealing.

Another common mistake is ignoring the thermal expansion of the pipe, so it is necessary to leave sufficient space in areas where the pipe approaches walls or floors. When installing into concrete or plaster, it is advisable to use protective sleeves that prevent direct contact of plastic with hard materials and allow movement during thermal expansion.

Incorrect pipe dimensions lead to inability to press or leakage.
Lack of fixings causes overload of threaded connections.
Dirt on the pipe surface damages the O-ring during pressing.
Incorrect tightening torque of threaded connections leads to leaks.

Frequently asked questions

Can I use a standard brass transition instead of PRESS?

Yes, but only if you correctly pass it through the pressing tool and use a special pressing ring, not a classic rubber ring. For easier and safer installation, it is always recommended to use a complete pressing set.

What to do if dripping occurs after pressing?

Immediately turn off the water supply, check whether the O-ring is damaged or whether the pipe was inserted incorrectly. The most common cause is damage to the ring by sharp pipe edges or dirt.

How long will a pressed joint with a transition last?

With proper installation and use of quality materials, a pressed joint will last for decades without the need for maintenance, as it has no moving parts and is resistant to corrosion.

PRESS transitions with external thread represent a reliable link between the modern pressing system and traditional radiator valves, provided they are installed with attention to cleanliness and precision. Adherence to these simple rules ensures flawless heating operation for years to come without the need for repairs.

Do you have a question about this topic?

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