What type of valve connection do I need: EK, VK and other standards
What type of valve connection do I need: EK, VK and other standards
When you start replacing a radiator valve or installing a new radiator, you will sooner or later come across abbreviations such as EK, VK, M30×1.5 or 1/2" and wonder what these markings mean and why so many different standards exist. This is not a coincidence or a manufacturer's invention – each of these markings describes a specific physical dimension, shape or function of the connection. If you choose the wrong combination, the valve simply won't fit, will leak, or the thermostatic head won't fit onto the valve body. This article will thoroughly explain all relevant standards so that you can order with precision and understand exactly what you are buying and why.
Why are there multiple connection standards at all?
There are several reasons, all historically justified. European heating technology developed in parallel in different countries, with German, Austrian, British and Scandinavian standards following their own paths for many decades. When the market opened and manufacturers began exporting, they had to maintain backward compatibility with older installations. As a result, at least three different systems for connecting the thermostatic head to the top of the valve (EK, M28, M30) and two dominant systems for connecting the pipe to the valve body (EK thread and the classic 1/2" BSP/G thread) are currently in use on the Slovak market.
In practice, this means that when replacing an old valve, you must measure or visually identify at least two things: (1) how the valve is connected to the pipe and (2) what standard is used for the top connection of the thermostatic head. Both values are equally important and the relationship between them is not automatic – a valve body with an EK top connection can have either an EK thread or a standard 1/2" G thread at the inlet/outlet, depending on the specific product.
What does the EK standard mean exactly
The abbreviation EK comes from the German term Einrohrkupplung or, according to some sources, simply denotes a standardized European conical connector (Eurokonus). In the context of radiator valves, EK is used in two different contexts, which is a source of confusion:
- EK as the top connection for the thermostatic head: This refers to an M30×1.5 mm external thread on the valve body. The thermostatic head or manual knob is threaded onto it and tightened. This is currently the most widespread European standard for thermostatic heads, and most heads on the market are directly compatible with M30×1.5.
- EK as a type of pipe connection: In product descriptions (e.g., "EK × 1/2"") the EK on the left side of the notation refers to a special conical unified connection used when connecting the valve to a radiator adapter or a fitting with an EK profile. It is a metric conical thread with a sealing cone, not a standard BSP thread.
So when you see a product labeled as Thermostatic radiator valve – straight, EK × 1/2", it is read as follows: the valve has a 1/2" thread on the pipe side (output to the pipe), which is a G 1/2" thread according to ISO 228 (i.e., a British pipe thread), and an EK connection on the radiator side – a special conical thread that is screwed into a radiator adapter with an EK profile. The thermostatic head is then threaded onto the M30×1.5 upper part of the valve.
VK – valve for two-pipe systems
The abbreviation VK comes from the German Ventilkörper or Voreinstellkörper and denotes a valve body specifically designed for two-pipe heating systems (a system with separate pipes for supply and return). VK valves have an adjustable hydraulic resistance – using the valve tip or a special screw, you can preset the maximum flow (so-called flow presetting, in English presetting).
This is a key difference compared to standard thermostatic valves for one-pipe systems: a VK valve functions as a combined thermostatic valve + control valve in one. Thanks to the preset flow value (kv, a flow coefficient), the system is hydraulically balanced without the need for a separate balancing valve on each radiator.
You will find products on the market such as VK valve, corner EK × 1/2", where the VK in the name indicates the function (two-pipe, with presetting), while EK × 1/2" describes the type of connection (just like with a standard thermostatic valve – EK connection to the radiator and 1/2" G thread to the pipe).
Thread standards for pipe connections: G 1/2", G 3/4", and others
The pipe connection of a valve (i.e., the side where the valve is screwed onto a copper or steel pipe, or a fitting) is marked according to the ISO 228 standard (Whitworth pipe thread, abbreviation G, older designation BSP – British Standard Pipe). The most common dimensions in radiator technology are:
- G 1/2" (DN 15): By far the most common size for radiator valves. The external thread diameter is 20.955 mm, with a pitch of 14 threads per inch. Almost all valves on the Slovak market for standard radiators are G 1/2".
- G 3/4" (DN 20): Used for larger radiators with higher output, for convectors or floor convectors. External thread diameter is 26.441 mm.
- G 1" (DN 25): Rare in radiator technology, more common for industrial applications or large convectors.
Important practical note: G thread is cylindrical (not conical), so the connection's tightness is not ensured by the thread itself, but by a sealing – either a flat Teflon washer or a rubber O-ring. If the sealing is missing or damaged, the connection will leak regardless of how tightly you screw the valve in. This is a fairly common mistake in DIY installation – more about it can be found in the article How to install a radiator valve yourself: step by step.
M30×1.5 – upper connection for thermostatic heads
This metric thread with an external diameter of 30 mm and a pitch of 1.5 mm is today the de-facto European standard for thermostatic heads. When manufacturers say that a head is "compatible with EK valves" or "universal for M30×1.5", they mean precisely this dimension. The vast majority of thermostatic heads on the market – regardless of whether they are made by Danfoss, Honeywell, Heimeier, IMI Heaton or another manufacturer – are primarily produced for M30×1.5.
The head is either directly slipped and screwed onto the valve body, or (in newer designs) locked in with a bayonet mechanism using an adapter. The M30×1.5 thread itself is on the outside of the valve body – the head has the corresponding internal thread. A stem (nub) protrudes downward from the head, which physically presses on the valve needle to regulate the flow.
Warning: there are also older or special valves with M28×1.5 (used e.g. in older Danfoss RA valves) or M32×1.5 (some industrial applications). These types are not directly compatible with M30×1.5 heads – an adapter is needed. Therefore, always check the exact dimension on the valve body before ordering a thermostatic head.
EK connection on the radiator side – how it differs from the standard G thread
This is the point where the most confusion arises when ordering. When a valve is connected to the radiator inlet (i.e., to the radiator connection, not to the pipe), either of the following can be used on the radiator side:
- Standard G 1/2" thread – the radiator has an adapter or a direct G 1/2" thread, and the valve is simply screwed on with a sealing.
- EK connection (Eurokonus) – the radiator has a conical special connection, and the valve has a matching conical counterpart on the radiator side. The tightness is ensured by the conical shape (cone) itself, not by a flat sealing. This system is mechanically more robust and less prone to leakage after multiple assembly/disassembly cycles.
In practice: modern panel (plate) radiators on the Slovak market – Radik, Korado, Stelrad, Purmo, etc. – usually have EK connections on both the inlet and outlet (with a plastic cap cover when delivered). Valves for these radiators have an EK connection on the radiator side, i.e., type "EK × 1/2". Older cast iron or finned radiators may have a standard G 1/2" thread – in these cases, either a valve with a G 1/2" × G 1/2" configuration or a transition adapter is needed.
Corner valves work the same way – the radiator connection is EK, the pipe connection is 1/2" G, but the outlet from the valve body is directed at a right angle (90°) instead of straight. More on when a corner or straight variant is suitable can be found in the article How to choose a radiator valve: straight vs. corner – what matters. If you prefer the straight variant, take a look at Thermostatic radiator valve – straight, EK × 1/2", and for the corner variant, you can find it here Thermostatic corner radiator valve, EK × 1/2".
SWING2 kits – when a complete set with precise connections is more convenient
A separate category consists of complete valve kits, where the manufacturer delivers the valve body, return valve, and connecting material in one package with guaranteed mutual compatibility. A typical example is SWING2 PN10 kit in straight configuration and SWING2 PN10 kit in corner configuration.
The designation PN10 indicates that the kit is certified for operating pressure up to 10 bar – which is more than sufficient for residential heating systems (a typical apartment system operates at 1.5–3 bar, and the maximum operating pressure at the safety valve is 3–4 bar). The same connection logic applies to these kits as to individual valves: the radiator connection is EK, and the pipe connection is G 1/2".
The SWING2 kit is particularly advantageous when replacing old valves on multiple radiators at once – it ensures design consistency, includes both valves (supply + return), and usually also contains the seals and connecting material. A more detailed analysis of when a complete kit is worth buying can be found in the separate article SWING2 kit: what it contains and when it is worth buying a complete set.
How to identify existing connections when replacing a valve
This is a purely practical question that even experienced plumbers address when entering someone else's installation. The procedure is as follows:
Step 1 – Top connection for the thermostatic head: Unscrew or remove the existing thermostatic head (usually it can be done by hand) and measure the external thread diameter on the valve body with a caliper. If you measure 30 mm – it is M30×1.5 (EK standard). If you measure 28 mm – it is M28 (usually old Danfoss). Note: the measurement must be accurate, do not estimate it.
Step 2 – Connection to the radiator: If the valve is already installed and you do not want to disconnect it without draining the system, check the radiator's technical documentation (type table, radiator model) or identify the connection visually. An EK connection has a characteristic conical shape of the transition part – it is not straight, but slightly narrowed towards the radiator. A standard G thread is uniformly cylindrical along its entire length with sharp thread edges.
Step 3 – Pipe connection: This is usually the easiest identification. If there is a fitting or valve with G 1/2" on the pipe, the new valve will also be G 1/2". Measure the external diameter of the existing pipe connection (20–21 mm = 1/2", 26–27 mm = 3/4").
Connection combinations – what is compatible with what
For clarity, we list the most common combinations you will encounter in practice:
| Valve type | Radiator connection | Pipe connection | Top connection (head) | Typical use |
|---|---|---|---|---|
| Thermostatic straight EK×1/2" | EK cone | G 1/2" | M30×1.5 | Modern panel radiators, pipe running under the floor directly under the radiator |
| Thermostatic corner EK×1/2" | EK cone | G 1/2" | M30×1.5 | Pipe running in the wall or channel, connection coming out from the side |
| Valve corner EK×1/2" | EK cone | G 1/2" | M30×1.5 | Two-pipe systems, hydraulic balancing required |
| Old valve G×G 1/2" | G 1/2" cylindrical | G 1/2" | M28×1.5 or M30×1.5 | Old finned / cast iron radiators, housing stock before 1990 |
| 3/4" valve | EK or G 3/4" | G 3/4" | M30×1.5 | Larger radiators over 2000 W, floor convectors |
Special cases and less common standards
Alongside the dominant EK and G 1/2" standards, there are situations where you might come across something non-standard. Here are the most common ones in practice:
Danfoss RA / RAL valves (M28×1.5): The Danish manufacturer Danfoss used proprietary top thread M28×1.5 for its RA series thermostatic heads for many years. These valves are still common in older apartment buildings in Slovakia. Only RA series Danfoss heads (and some universal ones with an adapter) fit them. You cannot directly fit a M30×1.5 head – you need an adapter or to replace the entire valve body.
Giacomini, FAR and other Italian valves: Some Italian products use metric connections, but with a different sealing profile. However, most are now adapted to M30×1.5 and EK compatibility, but always check the datasheets.
British BSP conical threads (BSPT/Rc): These differ from cylindrical BSP (G) in that the thread itself seals without a flat gasket. They are relatively rare in modern European heating technology, but you may encounter them in older British boilers or when importing equipment from the UK.
Direct valves for floor convectors (H valves): Some floor convectors require special double-H valves with a different body geometry. In these cases, EK and G 1/2" can be combined with other dimensions depending on the convector manufacturer.
Why the connection matters more than it seems
From experience, I know that an incorrect connection is not a problem that can be "fixed on site" without the right tools and parts. I have seen cases where a customer ordered a valve with a G 1/2" connection to the radiator, but the radiator had an EK connection. Result: either you need to buy an EK/G adapter (not always available in every store), or replace the entire valve. Both scenarios mean another visit or waiting for delivery.
An even more expensive mistake occurs when a valve with the wrong thread is "forced" to install and sealed only "temporarily" – this leads to water leakage, damage to the radiator thread (aluminum adapters are sensitive), and in the worst case, a flooded apartment. Therefore, correct identification of the connections before ordering a valve is absolutely essential.
If you are still unsure after a visual inspection, take photos of the existing valve from multiple angles (including the detail of the radiator connection) and send the photos to technical support – we can usually identify the connection from the photos. Alternatively, bring the old valve to the store – this is always the most reliable method.
PN10 and other pressure classes – what they mean for selection
Along with thread markings, you will also see pressure class markings on valves: PN6, PN10, PN16. PN (Pressure Nominal) indicates the maximum working pressure in bars for which the fitting is certified at a temperature of 20 °C. For residential heating, the following applies:
- PN6: Sufficiently suitable for older residential buildings with gravitational or low-pressure systems. Obsolete today.
- PN10: Standard for modern apartments and single-family homes. Working pressure up to 10 bars (at 20 °C), which is well above normal operating conditions.
- PN16: For commercial applications, larger buildings, or systems with higher pressure settings.
For a typical household, PN10 is always sufficient. SWING2 PN10 kits are therefore the right choice for 95% of apartment and single-family home installations.
Most frequently asked questions (FAQ)
I have a new Radik panel radiator – which valve fits it?
Panel radiators Radik (as well as Korado, Purmo, Stelrad and other European brands) have a standard EK connection on the inlet and outlet. You need a valve with an EK marking on the radiator side – typically an "EK × 1/2"" configuration. On the top part of the valve, a thermostatic head with an M30×1.5 thread is then mounted, which is now a universal standard. Whether you choose a straight or angled version depends on the direction of your piping.
I have an old cast iron radiator – will the same EK valve fit?
Not necessarily. Older cast iron fin radiators usually have a cylindrical G 1/2" connection, not a conical EK. You need a valve with a G 1/2" connection on the radiator side (i.e., a G 1/2" × G 1/2" configuration). An alternative is to install a G 1/2" → EK adapter, but this is an unnecessary complication if you simply order the correct type of valve. Always visually check or measure the existing valve before ordering.
Thermostatic head – do all of them fit on any valve?
Most common thermostatic heads on the market are designed for M30×1.5 (EK standard) and will fit all valves with this thread. Problems arise with older Danfoss valves with M28×1.5 – the standard M30×1.5 head does not fit these and you need either an adapter or a Danfoss RA series head. Always check the top thread of the valve with a measuring tool before purchasing the head. More details can be found in the article Thermostatic head: liquid-filled vs. gas-filled – which is better.
What is the difference between an EK valve and a VK fitting – I have a two-pipe system, which one should I buy?
If you have a two-pipe system (each radiator has its own supply and return pipe), the recommended type is a VK fitting, as it allows for pre-setting the flow (kV value) for each radiator individually. This is essential for hydraulic balancing of the system – without it, radiators closer to the boiler will be overheated and those further away will not be sufficiently heated. If you have a one-pipe system (all radiators are connected in series on one loop), a standard EK thermostatic valve without the pre-setting function is sufficient.
Can I replace only the thermostatic head without replacing the valve body?
Yes, if the same M30×1.5 (EK) thread remains – the thermostatic head can be unscrewed and re-screwed without the need to interfere with the plumbing/ heating system. It is not necessary to drain the system or close the main shut-off valves. The valve body remains in place, and you only replace the top part. Details on the procedure can be found in the article Replacing a thermostatic head without draining the system – is it possible.
Why does the catalog write "EK × 1/2"" and not the other way around "1/2" × EK"?
The convention for writing combinations of connections is: the first value = connection on the radiator side, the second value = connection on the pipe side. So EK × 1/2" means: the radiator side has an EK conical connection, the pipe side has a G 1/2" thread. The same logic applies to other fittings (elbows, couplings, etc.) – always check which part of the system corresponds to which value when reading the catalog.
Conclusion: why it pays off to pay attention to connections in advance
The topic of radiator valve connections may seem technically dry at first glance, but from the perspective of a successful installation, it is a critical piece of information. Every proper installation depends on the fact that the top connection of the valve (M30×1.5) matches the thread of the thermostatic head, the radiator side of the valve (EK or G) matches the radiator adapter, and the pipe side (G 1/2" or G 3/4") matches the existing piping. If you check these three parameters before ordering, the installation will proceed smoothly and without surprises.
If you are unsure – a situation even experienced DIYers find themselves in – take a photo of the existing installation, measure the threads with a caliper, and compare them with the values in this article. Alternatively, you can also check other articles in the Knowledge Center, such as Stuck or leaking radiator valve: causes and solutions or Maintenance and bleeding of radiator valves – how and how often, where you will find more practical information on how to properly care for valves.
The entire radiator valve category is designed so that you will find clear connection markings on each product – dimensions to the radiator and to the pipe, pressure class PN, sealing material, and compatibility with heads. If anything is still unclear, technical support is available.
Do you have a question about this topic?
Not sure how to proceed or dealing with a specific situation in your home? Write to us – we are happy to help.