How to set the weather compensation curve on calorMATIC or Thermolink controller

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Equithermal curve in calorMATIC and Thermolink control – complete guide to setting

The equithermal curve is the heart of every equithermal control. If it is set correctly, the boiler heats your house exactly as needed – without unnecessary overheating, without cooling down and with minimal gas consumption. If it is set incorrectly, you may have either cold or heat at home, but the boiler runs at full capacity even when it is not that cold outside – and this will be reflected in your bill.

In this article, we will take a closer look at what the equithermal curve actually is, how it is set specifically on the Vaillant calorMATIC and Protherm Thermolink controls, what values are suitable for different types of buildings and how to fine-tune the whole process so that your system works trouble-free year after year. If you are just starting with the term equithermal control, I recommend reading the article Equithermal control – what it is and how it works in practice, which you can also find in the Knowledge Centre.

What the equithermal curve actually tells the boiler

Simply put: the equithermal curve is a function that tells the boiler at what temperature to heat the water in the heating circuit at a given outside temperature. The colder it is outside, the higher the temperature the boiler maintains – and vice versa. This dependency is not linear in the absolute sense, although it may look like that at first glance; in real practice it depends on the physics of the building, heat losses, the mass of the structure and, not least, the type of heating system (radiators vs. floor heating).

The control receives information about the outside temperature from the outside temperature sensor (usually mounted on the north or northwest wall of the building). Based on this value, it calculates the required temperature of the heating water and controls the boiler accordingly. The whole principle is described in more detail in the article Equithermal control – what it is and how it works in practice.

On the calorMATIC and Thermolink controls, you set the curve with two main parameters:

Slope of the curve (Steilheit / slope) – indicates by how many degrees the temperature of the heating water will change for each degree of change in outside temperature. The higher the slope, the more sensitive the reaction.
Parallel shift (Parallelverschiebung / shift) – shifts the entire curve up or down, thus increasing or decreasing the boiler temperature at all outside temperatures uniformly.

Where to set the equithermal curve – overview of calorMATIC models

Vaillant calorMATIC is a family of controls that includes several generations and versions. Some models are wired, others are wireless (marked with an "f" at the end of the name), but the principle of setting the equithermal curve is basically the same for all – only the menu layout and parameter labeling differ in some firmware versions.

Among those we have in our range, these are the specific models:

Vaillant calorMATIC 360f – a wired model with basic equithermal control, suitable for simple systems
Vaillant calorMATIC 392 – a wired version with extended curve setting and multiple heating circuits
Vaillant calorMATIC 392f – wireless version of 392, functionally identical to the wired model
Vaillant calorMATIC 430 – a more advanced model with more extensive settings, support for multiple zones
Vaillant calorMATIC 430f – wireless version of 430

On the Protherm/Wolf side, the equithermal curve is set on the Thermolink controls, which are functionally compatible with Protherm boilers. The procedure differs in menu navigation, but the physical logic of the curve is the same. A comparison of these two families can be found in the article Vaillant calorMATIC vs. Protherm Thermolink – comparison of older controls.

Setting the equithermal curve on Vaillant calorMATIC – step by step

Access to the installer menu

The equithermal curve is a parameter that is only accessible to the installer – not to the regular user. The control is designed so that the average customer cannot accidentally change settings that affect the entire heating system. To enter the installer menu, you need a PIN code. The standard service code for Vaillant calorMATIC is 17, but it may differ on some older firmware versions. If you have changed and forgotten your PIN, the only option is to reset the device to factory settings.

Procedure for entering the menu (valid for most models of the 360, 392, 430 series):

Press the „i" (information / installer) button or the key symbol (depending on the specific model)
Enter the installer code 17 using the rotary selector or the ▲/▼ buttons
Confirm by pressing the OK button or the rotary selector
You have entered the installer menu – navigate through the items using the rotary selector

Finding the curve parameter in the menu

In the installer menu, look for a group of parameters related to the heating circuit – usually labeled as „Heating circuit" or „HK" (Heizkreis). Within this group, you will find:

Characteristic curve slope (slope of the curve) – parameter also referred to as „Steilheit" or simply a numeric code, e.g. d.12 or HK.Steilheit
Characteristic curve level (curve shift) – sometimes „Parallelverschiebung" or „Level"
Design temperature (design temperature) – the temperature of the heating water at the design outdoor temperature (e.g. -12 °C), from which the curve is derived

On the calorMATIC 392/392f model you will find these parameters directly on the first level of the installer menu under items d.10 to d.15 (the numbers may vary slightly depending on the software version). On the calorMATIC 430/430f the menu is more hierarchical – first select Heating circuit 1 (or 2, if you have a two-circuit system), then Settings, and there you will find the slope and level.

How to choose the correct curve slope value

This is the key question I encounter on most jobs. There is no single „correct" value – it depends on the type of building, the heating system, and sometimes even the customer's personal preferences. But we can give a solid starting point:

Panel apartment, original cast iron radiators, old windows – curve slope 1.4 to 1.6
Family house from the 80s–90s, standard steel radiators – slope 1.2 to 1.4
Newer house, well insulated, low-output radiators (fancoils or flat ones) – slope 0.8 to 1.1
Floor heating (low-temperature system) – slope 0.4 to 0.6, heating water temperature does not exceed 45 °C
Combined system (part floor heating, part radiators) – depends on the connection, usually 0.7 to 1.0 with a mixing valve regulation on the floor heating circuit

On calorMATIC controls the slope range is usually from 0.2 to 3.5 with a step of 0.1. On Thermolink it is similar, only the display may be different (sometimes as percentages or whole numbers 1 to 35 corresponding to values 0.1 to 3.5).

What is a parallel shift and when to use it

A parallel shift shifts the entire curve uniformly. It is an elegant tool for fine-tuning without having to change the slope. Practical example: the customer has a slope of 1.2 set, the house is well heated in freezing weather, but at mild temperatures (0 °C to +8 °C) it is 2 °C colder than desired. In this case, it is enough to shift the curve by +5 °C in parallel – the boiler will send 5 °C warmer water to the circuit at all outdoor temperatures, the slope remains the same.

Typical values for the parallel shift range from -15 to +15 °C on most calorMATIC models. The manufacturer sets 0 as the default. In practice, we most often move between -5 and +10.

Setting the heating curve on Protherm Thermolink

Entering the installer menu on Thermolink

Protherm Thermolink has a similar logic, but a slightly different menu navigation. The installer code is usually 0000 or 1234 – it depends on the generation and production year. When entering the menu, proceed as follows:

On some models, hold the MODE button or the „settings" icon for 5 seconds
Enter the installer code (0000 or 1234)
In the menu, look for the group of parameters „Heating" or „Vykurovanie"
Find the parameter „HC curve" or „Heating curve" – here you set the slope
Also check „Parallel shift" for the parallel shift

Thermolink sometimes displays the curve graphically directly on the display, which is a big advantage – you can see the set dependency immediately and visually evaluate it. Older Vaillant calorMATIC models show only numerical values, but calorMATIC 430 already has a graphical display of the curve as well.

Thermolink specifics when setting

Unlike calorMATIC, Thermolink sometimes has two separate parameters for the curve defined through two points – the heating water temperature at an outdoor temperature of -10 °C and the temperature at an outdoor temperature of +20 °C. From these two points, the control calculates the slope and shape of the curve. If you have such a model, it is enough to enter:

T_vyk at T_von = -10 °C – e.g. 70 °C for heavy radiators or 45 °C for floor heating
T_vyk at T_von = +20 °C – usually 20–25 °C (minimum temperature at which the boiler can still operate)

From these two points, the curve is uniquely defined. Simultaneous direct input of slope and shift is not possible with this type – it is a different philosophy, but the result is the same.

Practical scenarios from everyday customer practice

Scenario 1: House from 1987, cast iron radiators, poor insulation

The customer had a house heated by electricity, switched to a gas boiler Vaillant with regulation calorMATIC 392. The house is not insulated, windows are new (replaced 5 years ago), radiators are original cast iron, likely dimensioned for 80/60 °C. The external design temperature in the region is -12 °C.

Initial setting: slope 1.4, offset 0. After the first heating season, the customer reported that at temperatures around -5 °C the house was still slightly cooler, but at -15 °C the temperature was fine. Diagnosis: the curve has the correct "peak", but is slightly shifted low in the middle part. Solution: offset increased to +5 °C, slope remained 1.4. Result: satisfaction.

Scenario 2: New build from 2018, floor heating

The customer has a new house with floor heating and a condensing boiler Protherm with regulation Thermolink. The system was set by the builder to slope 1.2 – which is too high for floor heating. Result: the floor overheated at mild temperatures, the boiler went into the safety function limiting max temperature.

Solution: slope reduced to 0.5, maximum heating water temperature limited to 45 °C (parameter MaxVorlauf or Max. flow temperature). Offset set to +3 °C, so the house was comfortable even during transitional weather in spring and autumn. Gas consumption after this setting dropped by an estimated 12–15 % compared to the previous season.

Scenario 3: Older panel building, district heating replaced by individual boiler

Apartment building, where central heating was replaced by individual apartment boilers. Each apartment got its own boiler and regulation. Problem: adjacent apartments thermally influence each other, so the heat losses of one apartment are significantly lower than would correspond to the design temperature (neighbors are heating). Result with standard curve: it is too warm at home, the boiler unnecessarily overheats.

Solution: slope reduced to 0.9, offset to +2 °C. Maximum boiler temperature limited to 55 °C (cast iron radiators are sufficient). Result: comfort and lower consumption. In such cases I also recommend activating room correction (if the regulation supports a room sensor), so the regulation is independent of the curve according to actual room temperature.

Scenario 4: House with combined system – radiators upstairs, floor heating downstairs

This is one of the most complex cases. Most old calorMATIC and Thermolink regulations work with one curve for the whole system. If you have a combination, you either have to install a mixing valve with its own regulation on the floor heating circuit (which is the correct solution), or accept a compromise curve setting.

With a compromise: you set the curve for the radiator circuit (e.g. slope 1.1), and add a thermostatic mixing valve on the floor heating circuit set to a maximum temperature of 40 °C. This way the boiler works according to the curve for radiators, but the floor heating circuit is limited by a static valve. It is not ideal, but in practice it works well for most customers.

Common mistakes when setting the equithermal curve and how to avoid them

Mistake 1: Setting during transitional weather

The most common mistake I see: a technician comes to set the regulation in November, when it is +8 °C outside. Based on how the house is heated at this temperature, he sets the curve – and is satisfied in spring. But January comes, temperatures drop to -15 °C and the customer calls that it is cold at home. Problem: the curve was optimized for one point, but the slope was wrongly estimated.

Solution: Always set the curve based on at least two measurements – once during freezing weather (below -5 °C) and once during mild weather (+5 °C to +10 °C). If the situation does not allow it (e.g. installation in September), use tabular values and leave the customer instructions for fine-tuning the slope and offset, which they can do themselves (only offset, not slope – it is more sensitive).

Mistake 2: Wrong placement of the outdoor sensor

The outdoor temperature sensor must be on the north or northwest wall, at a height of 2–3 m, out of direct sunlight, in a wind-protected corner and away from exhaust vents or air leaks. If the sensor is on the south wall or near the doors, it measures distorted values – the regulation gets wrong information and the curve does not work properly regardless of the setting.

From practice: the customer had a calorMATIC 430f with an outdoor sensor behind a porch near the entrance doors. Despite the correct slope of the curve, it was sometimes too warm and sometimes cold at home – depending on how people moved around the doors and how the temperature in the entrance changed. After moving the sensor, the problem disappeared completely.

Mistake 3: Mixing room correction and equithermal regulation

Some models of calorMATIC and Thermolink allow connecting a room sensor and activating correction according to room temperature. If you turn this on without properly setting the equithermal curve, the system works in two layers of regulation at once – the equithermal curve sets the basic boiler temperature, the room correction then modifies it according to the actual room temperature. If the curve is set incorrectly and the correction is large, you can have an unstable system that oscillates.

Rule: First, set the control curve correctly (without room correction), then activate room correction with low sensitivity if necessary (±2 to 3 °C, not the maximum range).

Mistake 4: Ignoring the boiler's maximum temperature

The control curve can theoretically calculate a heating water temperature of 85 °C or even higher. However, the boiler has both hardware and software limitations on the maximum temperature. If you set a steep curve (slope 2.0+) and the boiler's maximum temperature is set to 75 °C, the curve will be "cut off" during freezing temperatures – which may look like the system is not working properly. Always check the parameter MaxVorlauf (maximum heating water temperature) in the installer menu.

Additional parameters that affect the behavior of the curve

The control curve is not the only parameter that controls the system's behavior. In the installer menu, you will find other settings that are closely related to it and should be set correctly:

Design outdoor temperature – the temperature at which the system is designed for full performance. For most of Slovakia, this is -12 °C, in mountainous areas -15 to -18 °C. This parameter affects the "anchoring" of the curve.
Minimum heating water temperature (Min. flow temp.) – the boiler will not go below this temperature, even if the curve suggests less. Important for condensing boilers (e.g., min. 25 °C), to prevent undesirable condensation in the heat exchanger.
Maximum heating water temperature (Max. flow temp.) – the upper limit for the curve. For floor heating, set it to 45 °C, for older radiator systems 70–80 °C.
Night setback – by how many °C the heating water temperature is reduced during the night mode. It is related to the curve – the regulation shifts the curve downward by the set value during the night reduction.
Antifreeze / Holiday mode temperature – the minimum heating temperature during longer absence. The curve is active in this mode as well, but at a very low level.

A complete installation procedure including sensor wiring can be found in the articles Installation and wiring of Vaillant calorMATIC step by step and Protherm Thermolink – installation and setting of basic parameters.

Adjusting the curve during operation – an iterative process

Correctly setting the control curve is an iterative process. No one can guarantee that the first attempt will be perfect – the building's physics, thermal bridges, solar gains, and occupants' habits affect real heat losses in a way that cannot be accurately modeled in advance without a detailed energy audit.

Recommended procedure for the first heating season:

Season start (September/October): Set the curve to the tabular value for the given building type. Leave the offset at 0.
November – first frosts: Check if it is comfortable inside when the outdoor temperature is around 0 °C. If it is cold, increase the offset by +3 °C. If it is warm, decrease the offset by -3 °C.
December/January – hard frosts: Check if it is comfortable inside at -10 °C and lower. If it is cold, increase the slope by 0.1 to 0.2. If it is warm, decrease the slope.
February/March – warming up: Check the behavior during transitional weather (+5 °C to +10 °C). If it is cold, slightly increase the offset. If it is warm, likely increase the offset downward or slightly reduce the slope.
After the first season: You have enough data for an accurate setting, which should last several years without change.

Important: allow at least 24–48 hours between each change and the next evaluation for the system to stabilize. The building has thermal inertia – the change will not be immediate, but gradual.

Connection to the boiler – what must be set correctly on the boiler side

The regulation calorMATIC or Thermolink communicates with the boiler either via eBUS (serial communication bus) or via classic two-pole switching (ON/OFF). If connected via eBUS, the regulation sends the boiler the required heating water temperature calculated according to the curve. The boiler respects this and modulates the power to maintain this temperature.

With ON/OFF connection, the regulation only switches the boiler on and off – and the boiler runs according to its own temperature setting, not according to the curve from the regulation. In this case, the control curve on the regulation does not work! This is a common source of misunderstanding – the customer buys an equithermal regulation, but it is connected only to ON/OFF terminals, and asks why the curve "does not show up".

For the correct function of the equithermal regulation, the regulation must be connected to eBUS terminals (on Vaillant boilers usually labeled "eBUS" or "2-8-9", on Protherm "eBUS" or "Bus"). Details on the connection can be found in the article Wired vs. wireless connection of old regulations to the gas boiler.

Frequently asked questions (FAQ)

What is the ideal slope value for a typical family house from the 70s–80s?

For a typical family house from this period with cast iron or steel radiators, without insulation or with old insulation, we recommend a starting slope of 1.2 to 1.4. The exact value depends on the actual heat losses – it is best to start at 1.2 and check during freezing weather whether there is enough heat in the house. If not, increase the slope to 1.4 or use a parallel offset of +5 °C.

Can an average customer change the equithermal curve themselves, or must an installer do it?

Technically speaking – most regulations have an installer menu protected by a PIN code precisely to prevent the average customer from changing it without knowledge. Some models allow the parallel offset to be changed directly from the user menu (without PIN), which is fine – it is a fine adjustment. The slope of the curve should really be changed only by an installer or an informed customer who knows what they are doing. An incorrectly set slope can lead to the house freezing or unnecessary energy costs.

Why does the house overheat in spring and autumn, but is warm enough in winter?

This is a classic sign of a too high slope of the curve in combination with a too high parallel offset. During freezing weather, the curve works well, but at an outdoor temperature of +5 °C to +10 °C, it still sends very hot water into the circuit. Solution: reduce the parallel offset by 3–5 °C, possibly also slightly reduce the slope. It also helps to activate room correction, so the regulation reacts to the actual room temperature and reduces the power when the house is already sufficiently warm.

Is there a difference in curve settings between the wired and wireless model of calorMATIC (e.g., 392 vs. 392f)?

Functionally no – the equithermal curve is set identically. The difference is only in the way of communication with the boiler (wired vs. wireless radio frequency). The curve parameters, the range of slope and offset values, as well as the procedure in the installer menu are identical for calorMATIC 392 and calorMATIC 392f. The same applies to the pair 430 and 430f.

The outdoor sensor is showing distorted values – what could be the cause?

The most common causes: the sensor is on the sunny side of the house (measuring the sun-heated temperature), the sensor is too close to the exhaust of a ventilation or air conditioning system, damaged cable (break or short – the regulation shows either -50 °C or +70 °C), oxidized contacts on the terminals. Check the resistance of the sensor – most Vaillant and Protherm sensors are type NTC 10kΩ (at 25 °C it should measure ~10 kΩ, at 0 °C ~33 kΩ, at -10 °C ~55 kΩ). If the resistance is outside these values, the sensor is damaged and needs to be replaced.

Is it worth investing in an equithermal regulation for an old boiler, or is a simple thermostat better?

It depends on the situation. An equithermal regulation makes sense mainly when the boiler can modulate its power (modern condensing or atmospheric boilers with electronic control) and when the building is larger or thermally unstable. For small apartments with one room and a simple system, a simple room thermostat is sufficient and cheaper. More on this topic can be found in the articles How to choose a regulation for an older Vaillant or Protherm boiler and Is it worth repairing an old regulation or is a replacement with newer models better.

Conclusion – what to take away from this article

Setting up the heating curve is not a one-time action – it is a living process that requires attention at least during the first heating season. The good news is that once you set it up correctly, the system will operate reliably for many years without the need for intervention. Key points to remember:

Choose the slope of the curve according to the type of building and heating system – higher for radiators (0.9–1.6), lower for floor heating (0.4–0.6)
Parallel shift is a tool for fine-tuning – it does not affect the shape of the curve, only its position
The outdoor sensor must be correctly placed – without this, no correct operation of the heating curve regulation is possible
The regulation must be connected via eBUS, not just ON/OFF, for the heating curve function to actually work
Optimize the settings iteratively during the season, not just once
Do not combine high room correction settings with a steep curve – the system will be unstable

If you are unsure about the settings for your specific system, or you suspect the curve was set incorrectly by a previous technician, or you are looking for a suitable regulation model for your boiler, check out models from the calorMATIC 430f or calorMATIC 360f series – each product description includes basic technical parameters including the curve range, and we are here if you have any questions.

Do you have a question about this topic?

Having trouble deciding or dealing with a specific situation in your home? Write to us – we are happy to help.