How to Identify the Correct Part Using the Boiler's Rating Plate and Serial Number

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Why the boiler's rating plate and serial number are the basis of every correct spare part selection

From practical experience, I know that most problems with incorrectly ordered spare parts don't arise from carelessness, but simply because the customer doesn't know where to look for the correct information. They call and say the pump in their boiler isn't working, give the brand, give the model – and think that's enough. But with condensing boilers, the situation is much more complicated. Manufacturers such as Viessmann, Bosch, Vaillant, Baxi, Ferroli, De Dietrich or Ariston have changed components and revised constructions over the years, selling identically looking boilers under the same commercial name but with completely different internal parts.

In this context, the rating plate and serial number of the boiler are something like the machine's birth certificate. They contain information that clearly identifies not only the model, but also the production batch, year of manufacture, power range, gas type, and often directly the spare parts group code. Without this data, any spare part selection is just guesswork – and with condensing boilers, the price of such a mistake is usually several dozen euros for an incorrectly ordered part, plus additional waiting time for the right one.

In this article, we'll look at where to find the rating plate, how to read it, what the individual abbreviations and numbers mean, how to decipher the serial number in terms of year of manufacture and version, and how to correctly use all this information when ordering spare parts and accessories for boilers.

Where to physically find the rating plate of a condensing boiler

This is the first practical question we need to answer, because the plate's location varies depending on the manufacturer, construction and generation of the boiler. A typical home customer opens the front cover of the boiler, looks inside, sees a flame or heat exchanger, and simply overlooks the rating plate because they're looking in the wrong place.

Most common locations of the rating plate

Inner side of the front cover – by far the most common location for Vaillant ecoTEC, Viessmann Vitodens or Baxi Luna boilers. The plate is attached directly to the plastic or metal casing, and you'll see it as soon as you lift or release the front panel.
Right side of the chassis – typical for some Bosch/Buderus models and De Dietrich boilers. The plate is protected from direct heat here and is usually more legible even after years of operation.
Left side of the chassis – less common, but found on older Ferroli models and some Spanish boilers sold under European brands.
Bottom or underside of the boiler – typical for floor-standing condensing boilers (e.g. Viessmann Vitodens 222-F). The plate is located at the bottom, which is practical during installation but less practical for later servicing.
Back wall of the boiler – occurs on boilers mounted on a bracket, where the back wall is not accessible without removing the boiler. In this case, the data is usually duplicated in the documentation or on an internal label.
On the heat exchanger or burner – some components have their own labels with a manufacturing date and serial number directly on the part's body. This is especially important when ordering the heat exchanger itself.

Practical tip: before you start searching for the plate on the physical boiler, check the warranty card or accompanying documentation for the boiler. Reputable installers typically write it in or stick a copy of the plate there. If the documentation is missing (which happens), the original plate on the boiler is the only reliable source.

What the rating plate contains – a complete breakdown

The rating plate of a condensing boiler is not just a sticker with the manufacturer's logo. It is a technical identification card regulated by European standards (primarily EN 677 for condensing boilers and the ErP Directive 2009/125/EC). Let's take a detailed look at all the fields the plate usually contains.

Commercial name and model type designation

This is the first line on the plate – for example "Vaillant ecoTEC plus VC 206/5-5" or "Viessmann Vitodens 100-W B1HF". It's important to understand that the abbreviations and numbers in the type designation carry specific technical meaning:

Vaillant ecoTEC plus VC 206/5-5: VC = Wandheizgerät Combi (wall-mounted combi = with domestic hot water heating), 206 = nominal power in kW × 10, i.e. 20.6 kW, /5 = fifth generation, -5 = natural gas G20
Viessmann Vitodens 100-W B1HF: 100 = product line, W = wall-mounted, B = condensing, 1 = generation, H = high efficiency, F = fan
Baxi Luna Platinum+ 1.24: 1 = generation, .24 = power 24 kW

The problem arises when the customer only knows the commercial name, not the full type designation. "I have a Vaillant ecoTEC" – that could be dozens of different models with different parts. Without the full type code, we won't get anywhere.

Serial Number (Seriennummer)

The serial number is a unique identifier of a specific boiler unit. Unlike the type designation (which is the same for all boilers of the same model), the serial number is unique. Manufacturers use it to:

Trace the exact production batch and manufacturing date
Identify potential batch defects (recall campaigns)
Verify warranty and service history
Precisely determine the version of internal components (PCB revision, burner version, heat exchanger type)

The structure of the serial number varies by manufacturer, but typically includes an encoded year and week of manufacture. For example, for Vaillant boilers, the first four digits of the serial number in the format WWYY represent WW = week and YY = year. Serial number 2318xxxxxxx therefore means: week 23, year 2018.

Power parameters on the plate

The rating plate must state the boiler's power range. For condensing boilers, these are typically two power values:

Rated heat output (Q nom) – maximum output at full load, e.g. 24 kW
Minimum heat output (Q min) – output at modulated minimum power, e.g. 7 kW
Output in condensing mode – higher than Q nom due to the use of latent heat, e.g. 26.2 kW

These values are key when choosing components that are power-sensitive – for example, the expansion vessel (its volume depends on power and the amount of water in the system), the safety valve (opening pressure must match the parameters), or the circulation pump.

Gas type and operating pressure

The plate always states the gas type the boiler is set for: G20 (natural gas, Slovakia), G25 (natural gas with lower calorific value, some regions of Central Europe) or G30/G31 (propane/butane for LPG boilers). This is important when ordering burners, nozzles and injectors – these parts are heat-value specific and not interchangeable.

Appliance category

E.g. "II2H3P" – this abbreviation indicates which gas types the boiler is approved for. II = category II (suitable for two gas groups), 2H = natural gas H, 3P = propane. This is particularly relevant for repairs in areas where the gas network is changing or when converting a boiler to LPG.

How to read and decode the serial number for different manufacturers

Each manufacturer has its own serial number logic. Here is an overview of the ones we encounter most often on the Slovak market.

Vaillant

Format: WWYY + 7-digit production number. WW = production week (01–52), YY = last two digits of the year. Example: 1521xxxxxxx = week 15, year 2021. Vaillant has a system where different PCB (control board) versions were introduced at specific serial numbers – for example, some ecoTEC plus revisions from series approx. 2317xxxxxxx have a different control board version than older units, and thus a different spare part number for the PCB.

Viessmann

Format: 7-digit number without direct date encoding in a visible structure, but with an internal database. The year of manufacture for Viessmann boilers is more reliably determined via the boiler's service menu (a diagnostic parameter shows the manufacturing date) or via the Viessmann online spare parts system by entering the serial number.

Bosch / Worcester Bosch / Buderus

Format: Combined code starting with a letter for the production plant, followed by a numeric code with the manufacturing date in the format YYMMDD or YYDDD (year, Julian day). Bosch also has an FD number system (Fertigungsdatum = manufacturing date), which is listed on the plate as a separate field "FD", e.g. "FD9701" = January 1997.

Baxi

Format: Typically a 10–13 digit serial number. The first two or four digits encode the year and week of manufacture, similar to Vaillant. Baxi also has a model code (MC) number, which is important when ordering parts through Baxi catalogues – the MC number is found on the plate as a separate field.

Ariston / Chaffoteaux

Format: Ariston's serial number starts with a production plant code (e.g. IT = Italy, CZ = Czech Republic) followed by a date code. Ariston has a proprietary online portal "Ariston Technical", where entering the serial number gives you an exact exploded view of the boiler with part numbers.

Step by step: how to correctly identify a part according to the rating plate

Now let's move on to the practical procedure. This is the process we use for every question about a spare part, and I recommend following it in this order.

Step 1: Document the rating plate with a photo

Photograph the rating plate with your smartphone so that all text fields are legible. Common mistake: a blurry photo where the serial number is illegible, or a photo of only part of the plate. Photograph the entire plate, in good lighting, ideally with the smartphone flash turned off (a glossy plate surface will cause glare). If the plate is damaged, faded or partially illegible, record at least the fields you can see and supplement them from the boiler's service documentation.

Step 2: Identify the complete type designation of the model

From the photo, write down the complete type designation – not just the commercial name, but the entire code including numeric suffixes. For example, not "Vaillant ecoTEC plus", but "Vaillant ecoTEC plus VC 206/5-5 (H)" or the exact code as stated on the plate.

Step 3: Write down the serial number and decode the year of manufacture

Using the manufacturer table above, decode the year (and week, if applicable) of manufacture. This is important because some parts were changed within the same model, and spare parts suppliers classify them precisely by serial number. Practical example: a Vaillant ecoTEC plus VC 206/5-5 manufactured before 2015 has a different primary heat exchanger seal than units manufactured after 2015 – both look the same, but the codes and dimensions differ.

Step 4: Identify the faulty part (what failed)

Before ordering, you must know which part you're looking for. If you haven't already, check out the article Most common condensing boiler faults and which parts fail first, where you'll find an overview of the most commonly replaced components according to symptoms. Knowing that "the boiler is dripping" is not enough – you need to know whether it's dripping from the primary heat exchanger, the secondary domestic hot water heat exchanger, the expansion vessel, or the hydraulic unit.

Step 5: Find the spare part number in the exploded view catalogue

Every reputable condensing boiler manufacturer has exploded view catalogues available (exploded diagrams of the boiler with part numbers). These catalogues are available:

Directly on manufacturers' websites (Vaillant ProCenter, Viessmann ProNet, Bosch Pro portal)
Via distributors' technical portals
In printed form in the boiler's installation documentation

In the exploded view, you'll find the specific position of the part (e.g. position 07 = circulation pump) and the associated spare part number (e.g. 178977 for Vaillant). This code is the basis for the order.

Step 6: Verify compatibility with the serial number range

In catalogues, a part is usually assigned with a note on validity: "valid for SN from XXXX to YYYY" or "valid from FD YYMM". Check whether your serial number falls within this range. If not, look for an alternative spare part number for your range.

Typical mistakes in identifying a part – examples from practice

Years of work in selling boiler spare parts have given us a collection of situations that didn't work out. Not to pillory anyone, but because these examples are the best teacher.

Example 1: "I have a Vaillant 24 kW, I need a pump"

A customer ordered a circulation pump for a "Vaillant 24 kW". There were two options offered for the ecoTEC plus 24 kW – an older and a newer version. The customer chose the cheaper one. Upon delivery, it turned out that his boiler was an ecoTEC pro (not plus), manufacturing year 2009, where Vaillant still used a Grundfos UPM2 15-75 pump instead of the later Wilo Stratos Para 15/1-7. The pump was visually similar, but the hydraulic flange and electrical connector were different. Result: return, waiting, delay.

Solution: when ordering, it was enough to state the full type designation "VC 206/2-5" and the serial number, from which it was clear that this was a boiler from before 2012 with the corresponding pump version.

Example 2: Correct model, wrong gas type

A customer in the Trnava area needed to replace the burner nozzle in a Ferroli Bluehelix Tech boiler. The boiler was set up for propane (LPG), but the customer didn't mention this when ordering because he thought it wasn't important. He received a nozzle for natural gas G20 – the nozzle opening diameter for G20 is approx. 1.3–1.5 mm, while for propane G31 it's only 0.7–0.9 mm (depending on output). Installing the wrong nozzle would cause the boiler to burn incorrectly, potentially leading to dangerous overheating.

Solution: always state the gas type from the rating plate (G20/G25/G30/G31) when ordering any part related to combustion.

Example 3: A "same output" replacement part from another manufacturer

A customer with a De Dietrich boiler ordered a "compatible" control board from another seller – a cheaper alternative. This board had identical mechanical dimensions and seemingly the same software profile. However, on first startup, the boiler reported error F75 (pressure sensor problem). It turned out that the replacement board had a different reference voltage for the pressure sensor, so the boiler failed to communicate correctly. The original spare part solved the problem immediately.

You can read more on this topic in the article Original vs. non-original boiler spare parts – is it worth saving money?, where these situations are analysed in detail.

Online tools and databases for finding a part according to the rating plate

Condensing boiler manufacturers and distributors have invested heavily in recent years in online tools that make it easier to identify parts. Here is an overview of the most practical ones.

Official manufacturer portals

Vaillant Spare Parts Finder – after entering the type designation, it displays an interactive exploded view with the option to add the part directly to the cart. The serial number code automatically filters part versions.
Viessmann Online Parts Catalogue – divided into service partners (full access) and the public (limited access). Spare part numbers are visible, but the order must go through an authorised distributor.
Worcester Bosch Spares – a relatively open system where entering the GC (Gas Council) number or type code gives you a complete list of parts with prices.
Baxi Spare Parts – a similar system, working with the MC number from the rating plate.

Third parties and aggregators

There are also independent spare parts databases such as Sontex, Espares or Heatershop, where you can search cross-reference by manufacturer's spare part number and equivalent numbers. These platforms are useful for finding alternative suppliers, but I always recommend verifying compatibility with the serial number range, not just the type designation.

Special situations: a boiler with an illegible plate or unknown origin

In practice, it happens that the rating plate is illegible (damaged by water, faded, physically cut off by a previous "clever" installer). What then?

Alternative sources of identification

Boiler service menu – most modern condensing boilers display the type designation and software version in the diagnostic menu. For example, a Vaillant ecoTEC shows the type code in menu d.1 and the serial number in d.2.
Barcode on the boiler – many boilers have a barcode attached to the hydraulic block or frame in addition to the rating plate, where the serial number is encoded in EAN or Code 128 format. You can scan this code with an ordinary smartphone app.
Warranty card and installation documentation – if the boiler was installed by a reputable installer, the documentation should contain a copy of the plate or at least a record of the type designation and serial number.
Distributor or manufacturer database by address – Vaillant and Viessmann have internal databases where installed boilers may be recorded by address. An authorised service technician can perform this kind of lookup.
Physical identification of components – an experienced technician can estimate the boiler's series based on specific parts (pump, combustion chamber, heat exchanger). It's slow, but when other sources are missing, it helps too.

Rating plate vs. labels on individual components

In addition to the boiler's main rating plate, it's important to know that individual key components also have their own labels or production codes. This is particularly relevant in situations where you're replacing a component that has already been replaced once before and may have been substituted with a replacement or different version.

Circulation pump – has its own label with type, production number and hydraulic parameters (max. flow rate l/hour, maximum pressure in m.w.c.). This data is crucial if you order a pump not by spare part code, but by hydraulic equivalence.

Control board (PCB) – usually has a hardware and software version printed on it. For example, a Vaillant PCB may have a designation "VCB3.08" where VCB = board type and 3.08 = version. This information is key for the interchangeability of boards within one generation of boilers.

Primary heat exchanger – usually has a production code, and for stainless steel exchangers also a material batch number. When ordering a heat exchanger, it's essential to state the spare part number, because exchangers with the same external dimensions may have a different number of layers/flow passes.

You can read more about how to properly care for these components and prevent their premature failure in the articles Maintenance and servicing of a condensing boiler – which parts to replace regularly and How to prevent premature wear of condensing boiler parts.

How to communicate with a seller when ordering a spare part

When you contact a spare parts seller, whether by phone or via an e-shop, the rule applies: the more information you provide, the faster and more accurate your order will be. Here is a recommended standard for communication:

Complete type designation of the boiler (from the rating plate, not from memory)
Boiler serial number (complete, without omitting digits)
Year of manufacture (if you've decoded it, or at least an estimate)
Gas type (G20 / G30 / G31)
Description of the fault (what's happening, what error code the boiler displays)
Identification of the part you need to replace (by position or function)
If you've found the spare part number yourself – state it, the seller can verify it

A good seller should be able to clearly identify the correct part based on this information. If a seller suggests a part based only on the boiler's commercial name without verifying the serial number and year of manufacture, be cautious – this may be a generic approach that will fail for some models.

You can find more practical advice on choosing the right spare part, including the question of original versus replacement parts, in the article How to choose the right spare part for a condensing boiler – what to watch out for.

What to do after the warranty period – identifying a part on older boilers

An older boiler out of warranty presents a special challenge: the rating plate may be damaged, some spare part numbers may have been discontinued by the manufacturer, and you need to look for replacement or compatible substitutes. In this context, the serial number is even more important, because the manufacturer can use it to determine exactly which version of the component was originally in the boiler and can recommend an approved replacement.

If your boiler is more than 10–12 years old, I recommend consulting the manufacturer's technical department or an authorised distributor before ordering any major part, to check whether the model is still serviceable and what the availability of key spare parts is. You can read more on this topic in the article Condensing boiler spare parts after the warranty period – how to proceed and where to buy.

Frequently Asked Questions (FAQ)

Is it enough to know just the commercial name of the boiler (e.g. "Vaillant ecoTEC plus 24 kW") to order a spare part?

No, the commercial name is not enough. Dozens of different variants with different internal components, control board versions, pump types and heat exchangers may be sold under the same name. For reliable part identification, it's essential to provide the complete type designation from the rating plate (e.g. VC 206/5-5) and the serial number, from which the year and production series of the boiler can be determined.

Can I find the boiler's serial number even without the rating plate?

Yes, there are several alternative sources: the boiler's service diagnostic menu (most modern boilers display the serial number in the menu), a barcode attached to the hydraulic block or frame of the boiler, the warranty card or installation documentation. As a last resort, an authorised service centre can help, as they can look up the boiler in a database by installation address.

Why does the spare part differ for boilers of the same output but different years of manufacture?

Condensing boiler manufacturers continuously revise their designs – improving reliability, changing component suppliers, addressing batch issues. A part that was in a boiler manufactured in 2010 may be replaced in 2018 by a component from a different subcontractor with different connector dimensions, seals or hydraulic connections. That's why spare parts catalogues are always tied to a range of serial numbers, not just the type name.

Where can I find an exploded view (exploded diagram) for my boiler?

The primary source is the official websites of manufacturers (Vaillant Spare Parts Finder, Viessmann ProNet, Bosch Pro portal, Baxi Spare Parts). Many of these require registration as a service partner. For ordinary customers, they are available through authorised distributors or directly upon request from a spare parts seller. Some catalogues are also available as PDF downloads on manufacturers' websites in the technical documentation section.

What do the abbreviations G20, G25, G30, G31 mean on the rating plate?

These are European designations for gas type: G20 = natural gas (methane, calorific value approx. 34.02 MJ/m³, predominant in Slovakia), G25 = natural gas L (lower calorific value, approx. 29.25 MJ/m³, used in some parts of Central Europe), G30 = butane (LPG), G31 = propane (LPG). These codes are crucial when ordering combustion-related parts – burners, nozzles, control valves – where a mix-up can lead to dangerous boiler operation.

Can I order a part myself in case of a fault, or should I leave it to a professional?

You can identify and order a part according to the rating plate and serial number yourself – no special expertise is required, just follow the procedure described in this article. Actually replacing the part is a different matter: some tasks (e.g. replacing the expansion vessel, filter or anode) can be handled by a skilled DIYer, while others (burner replacement, heat exchanger cleaning, combustion recalibration) require an authorised service technician. You can read more about what's safe to do yourself in the article Installing condensing boiler spare parts – what you can do yourself and what to leave to a professional.

Conclusion: the rating plate is the basis – don't underestimate it

The rating plate and serial number of a condensing boiler are the information at the start of every correctly solved spare part problem. Invest five minutes documenting them – photograph the plate, write down the numbers, save them to your phone or the boiler's documentation. When the boiler loses power or starts dripping on a freezing night, those two minutes of searching for the photo will save you a day of waiting for the right part.

The entire range of spare parts and accessories for condensing boilers at atria.sk is organised so that you can state the type designation and serial number when ordering – and our technicians will help you identify exactly the right part for your boiler. Because with condensing boilers, it truly holds true: getting the right part the first time saves time, money and nerves.

Do you have a question on this topic?

Can't decide or dealing with a specific situation in your household? Write to us - we'll be happy to help.