Calibration and adaptation of programmable head after installation

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Calibration and adaptation of the programmable head after installation

Installing a programmable thermostatic head on a radiator is only the first step. Most users think it's enough to screw on the head, set the program, and that's it. In practice, it's not that simple – every programmable head needs to go through a calibration and adaptation process to the specific valve, space, and thermal conditions of the room after installation. If you skip this step or do it incorrectly, the head will either overheat the room or, on the contrary, not reach the set temperature, or it will constantly "oscillate" around the target value without actually stabilizing.

In this article, we will go through the entire process from the moment you mount the head on the valve until the regulation runs smoothly and accurately. If you're still in the selection process, I recommend first reading the article How to choose a programmable head for a radiator and possibly also Installation of a programmable head on a radiator step by step, where the mechanical installation steps, including adapters, are described in detail.

What is valve calibration and why is it necessary

Every programmable thermostatic head contains an electric drive – typically a small stepper motor or a thermo-electric actuator – that physically moves the valve stem. This drive does not see inside the valve, does not know where the stem is located, or what the total lift of the specific valve is. That's exactly what calibration is for: the head measures in a controlled process where the mechanical stop (fully closed position) is and where the other stop (fully open position) is, and from this range it calculates how to set the drive for each desired temperature.

The lift of the valve stem is not the same for all valves. Common ranges are 2 to 4.5 mm, while older cylindrical valves such as Heimeier or Danfoss RA can have a lift of up to 4.8 mm. Newer modern valves are usually shorter in construction. If the head assumes a standard lift, for example 3.5 mm, but the actual valve has a lift of 2 mm, the drive will be set too far, the stem will be mechanically jammed, and it will either damage the gearbox or simply not close/open properly.

Therefore, most modern programmable heads – including models such as Elektrobock HD10 and Elektrobock HD20 – perform automatic calibration after the first installation. This usually takes a few seconds or minutes after inserting the batteries, and you can recognize it by the characteristic movement of the drive (a soft click or buzz) and the indicator on the display (a blinking key symbol, a cogwheel, or the abbreviation "CAL").

Automatic calibration step by step

The calibration procedure varies slightly depending on the manufacturer and model, but the principle is always the same. Here is a typical sequence as I have observed from dozens of installations:

Mounting on the valve: The head is screwed or clicked onto the valve. At this point, the drive is still without power or in a neutral position.
Inserting batteries / turning on: After inserting the batteries, initialization starts. A welcome sequence or a blinking symbol usually appears on the display.
Movement to the stop: The drive slowly moves downward until it hits the mechanical stop of the valve. The slight resistance is detected via current increase or motor response. This position is recorded as "zero" (fully closed).
Movement to the fully open position: The drive moves in the opposite direction and similarly finds the second stop. The maximum lift value is recorded.
Calculation and saving: The microprocessor calculates the linear (or non-linear) transfer characteristic: each percentage of opening corresponds to a precisely defined number of motor steps. These data are saved in memory.
Confirmation: The current temperature or set temperature is displayed on the display, and the head enters normal operation.

The entire process usually takes 30 seconds to 3 minutes. During calibration, do not move or adjust the head – let it complete. If you interrupt the calibration (by removing the batteries or performing a hard reset), you will have to repeat it. Some heads require manual initiation of calibration through the menu after an interruption.

Manual calibration initiation – when and how

In addition to the initial calibration, there are situations when it is necessary to repeat the calibration manually:

Moving the head to another radiator or a different type of valve
Replacing the valve on the same radiator
After service work on the heating system (descaling, pressure test)
If the head stops regulating properly – either not heating or not closing
After long-term storage (e.g., summer heating shutdown)
After replacing batteries, if some models lose calibration data (rare, but it can happen)

The procedure for manually initiating calibration varies by model. For SALUS PH 55 and SALUS PH 60, it is typically a long press of a specific button or a combination of two buttons according to the manual. For Elektrobock models, calibration is initiated via a service menu or a hardware reset (pinhole reset). Always read the manual before performing manual calibration – the procedures are specific, and incorrect steps can accidentally reset the set weekly program as well.

Adaptation to the room – what happens after calibration

Calibration is a mechanical process. Adaptation is a thermal and algorithmic process that follows it and usually lasts from 1 to 5 days. During this period, the head "learns" the thermal characteristics of the room: how quickly the room heats up at a given valve opening, how quickly it cools down, what is the thermal inertia of the walls and floor, and what is the influence of the outside temperature through the windows.

Modern programmable heads use a PID control algorithm (Proportional-Integral-Derivative) or a simplified version of it. This algorithm calculates the difference between the current temperature and the desired temperature (error), integrates the history of this error over time, and derives the trend of change. Based on these three components, it calculates how much the drive should open the valve.

During the first few hours after installation, you may observe several "non-standard" phenomena, which are completely normal:

Overheating at first start: The head does not yet know how quickly the room heats up and may open the valve too much, causing the temperature to overshoot the set point by 1–2 °C. This is gradually corrected.
Slow temperature reaching: Conversely, the algorithm may be initially conservative and the temperature may rise more slowly than expected.
Frequent drive switching: During learning, the drive opens and closes the valve at short intervals – you may hear this as a faint clicking. This is normal.
Unstable displayed temperature: The temperature sensor in the head measures the air temperature in the immediate vicinity of the head, which is not the same as the temperature in the center of the room. The displayed value may therefore be slightly different from the temperature measured by a reference thermometer.

Setting the sensor offset (temperature offset)

This is one of the most important and most often neglected functions. The temperature sensor in the programmable head measures the temperature on the radiator itself, or in its immediate vicinity. This temperature is almost always higher than the temperature in the center of the room – the difference can be 1 to 5 °C, depending on the radiator's placement, the presence of a cover (decorative grid), draughts, and ventilation.

Therefore, most heads allow setting a temperature offset – a correction that shifts the displayed (and regulated) temperature by a defined value. The procedure is simple:

Let the room stabilize at a stationary temperature – best in the morning after a night with a constant setting. Turn off all heat sources except the given radiator for 30–45 minutes.
Place a reference thermometer (a calibrated digital thermometer) in the center of the room at a height of 1–1.5 m from the floor, away from windows and walls.
Read the temperature from the reference thermometer and the temperature displayed on the head.
Enter the difference as an offset in the head's menu. If the head displays 22 °C and the reference thermometer shows 20 °C, set the offset to –2 °C.

With the model Elektrobock EMF-1, which functions as an external temperature sensor for other control systems, this problem is eliminated – the sensor is located directly in the room, not on the radiator. However, even in this case, verify that the sensor is placed correctly and is not affected by direct sunlight or airflow from ventilation.

Setting up hysteresis – how to prevent "hunting" around the target value

Hysteresis (sometimes called a "dead zone" or deadband) is a temperature range around the target value in which the head does nothing – neither adds nor removes heat. Example: if the target temperature is 20 °C and the hysteresis is 0.5 °C, the valve will start to close only at 20.5 °C and open only at 19.5 °C. Without hysteresis, the head would constantly switch on and off with every minor deviation.

A typical factory-set hysteresis value is between 0.3 and 1 °C. Lower hysteresis = more precise regulation, but frequent switching of the actuator and higher battery consumption. Higher hysteresis = less precise regulation, but longer battery life and smoother actuator operation. For most residential rooms, the optimum is somewhere between 0.5 and 0.8 °C.

If you notice in your room that the head is constantly clicking and the radiator alternately hums and quiets down at intervals of a few minutes, consider slightly increasing the hysteresis. On the other hand, if the temperature in your room fluctuates by 2–3 °C up and down, the hysteresis is set too high.

Anti-Frost function and valve protection – setting and verification

Almost every programmable head contains two protective mechanisms that need to be verified and possibly set after installation:

Frost protection (Anti-Frost / Frost Protection): If the room temperature drops below a defined value (typically 5–8 °C), the head automatically opens the valve regardless of the set program. This function protects the pipes and radiators from freezing. Verify that it is activated and set to the correct value. For chalets, recreational buildings and balconies, I recommend setting a higher limit – for example 8 °C – because temperature drops are faster there.

Valve jam protection (Open/Close Protection, Valve Protection): If the valve remains in the same position for a long time – typically in summer, when heating is not in operation – it may jam in that position. To prevent this, the head automatically performs a full actuator stroke once every few days (usually every 7–14 days): the valve opens, waits for a while and closes. This function should always be activated, especially in systems where the radiator is used seasonally.

Testing after calibration – practical verification procedure

After completing the calibration and basic setup, I recommend performing a simple verification test. I do this test for every customer and it saves a lot of unnecessary complaints and service visits.

Valve closing test: Set the target temperature to 5 °C (or the minimum value). Wait 3–5 minutes. Touch the radiator – it should cool down significantly or remain cold (if it was already cold). If the radiator remains hot, the valve did not close. Possible causes include: incorrect calibration, the adapter is not properly mounted, the valve insert is damaged or clogged with limescale. More about faults can be read in the article Programmable head does not heat or close – common faults and solutions.

Valve opening test: Set the target temperature to 30 °C (maximum). Wait 3–5 minutes. The radiator should start to heat up – the top should be significantly warmer than the bottom. If the radiator does not heat up, the problem is likely a closed shut-off valve, low boiler temperature or a jammed head actuator.

Accuracy of the sensor test: Let the room stabilize (at least 30 minutes without opening doors and windows), read the temperature from the head and compare it with a reference thermometer. After correct offset setting, the difference should be at most ±0.5 °C.

Common calibration errors and their solutions

Over the years of experience, I have seen several recurring errors that cause calibration to be incorrect or not performed at all. Here are the most common ones:

Head mounted on a valve with an adapter that is not tightened: If the adapter is not firmly clicked or screwed onto the valve and the head, the actuator measures the lift of the adapter, not the valve. During calibration, it may seem that everything went smoothly, but the regulation works chaotically. Always verify that the entire connection is secure before calibration. More about adapters can be read in the article What thread does a programmable head need – M30x1.5 and adapters.

Calibration with the boiler turned off or a cold system: Technically, this is not a problem – the mechanical calibration will proceed correctly. The problem arises during the subsequent functional test: if the boiler is off, you cannot verify whether the valve correctly opens and closes the heat flow. Always test the function only after the boiler has been started.

Actuator jammed due to an old/rusty valve: On old radiators (15+ years), the valve insert may be corroded and the actuator may not have enough force. Calibration will find the jam too early, because the valve cannot be fully opened physically. Solution: replace the valve insert before installing the new head. This is a sneaky fault, because the calibration appears successful from the outside, but in reality the valve never reaches full opening.

Incorrect batteries or low voltage during calibration: If you insert weak batteries (e.g., old or partially discharged), the actuator may not have enough power to overcome the valve resistance. Calibration will end with an error or appear to complete, but with an incorrect range. Always use new batteries when installing. For more information about batteries and their lifespan, see the article Battery replacement in a programmable head and power longevity.

Interfering with the head during calibration: Touching moving parts, pressing buttons, or moving the radiator during calibration can cause incorrect recording of the stops. Let the head work without interference.

Special situations: calibration when replacing a head with a manual one

If you previously had a manual thermostatic head and are replacing it with a programmable one, remember that a manual head usually holds the valve in a specific position – partially open, partially closed. After removing it, the valve stem may move freely according to the internal spring of the valve and when fitting the new head, it may be in a completely different position than expected. Before fitting the new head, check that the valve stem is not stuck in an extreme position – you can do this by gently pressing with your finger: the stem should be movable with slight spring resistance.

A detailed comparison of manual and programmable heads in terms of function and installation can be found in the article Programmable vs. manual thermostatic head – which one is worth it.

Optimal environment for regulation accuracy

Even if the calibration is performed perfectly, the accuracy of regulation depends on the environment. A few practical tips from field experience:

Radiator must not be covered: A decorative grille or radiator cover significantly changes the temperature around the head. If you have a cover, you must set a higher offset – up to 4–5 °C in extreme cases. Alternatively, use a head with an external sensor, such as the Elektrobock EMF-1.
Curtains must not cover the head or radiator: A curtain traps warm air near the radiator and the sensor in the head records a higher temperature than the actual room temperature. Result: the head closes the valve too early.
Furniture must not block air flow around the radiator: A sofa or cabinet right in front of the radiator dramatically reduces the effectiveness of regulation. Heat does not rise into the room, but remains behind the furniture.
Windows should be closed during regulation: An open window in winter means the room cannot reach the target temperature. The programmable head opens the valve fully, the boiler works at maximum, but the temperature still does not drop. Some heads (e.g., SALUS PH 60) have a window-open detection function – in case of a rapid temperature drop, the valve is automatically closed.

Connection between calibration and the weekly schedule

Only after verifying correct calibration and temperature offset does it make sense to set the weekly schedule. Setting the schedule earlier is pointless, because you are setting target temperatures for specific time periods, and if the sensor is inaccurate or the valve is not properly calibrated, the schedule will function differently than intended. A detailed procedure for setting the weekly schedule can be found in a separate article Setting the weekly schedule on a thermostatic head.

A short summary of the correct order after installation:

Mechanical installation + valve calibration (automatic or manual)
Function test (opening and closing the valve)
Setting the temperature offset
Verifying hysteresis and possible adjustment
Activating protective functions (anti-frost, valve protection)
Setting the weekly schedule
Monitoring behavior during the adaptation period (1–5 days)

Calibration in systems with multiple heads

In family homes or apartments with multiple radiators in different rooms, the calibration of each head is a separate process – each valve has a different type, degree of wear, and resistance. There is no "synchronization" between heads, each calibrates its own mechanical characteristics independently.

What is important with multiple heads: setting temperatures and schedules should be based on a consistent reference measurement. It is not enough to calibrate each head separately without a reference thermometer – you may end up in a situation where one room is regulated at 20 °C and another effectively at 22 °C despite the same target setting. Therefore, I recommend after calibrating all heads to perform a measurement in each room with a reference thermometer and adjust the offsets accordingly.

If you are looking for a comparison between models suitable for different types of rooms or larger systems, see the article Elektrobock vs. SALUS – comparison of programmable heads, where these aspects are discussed in detail.

Most frequently asked questions (FAQ)

How long does calibration take and what should I do during it?

Automatic calibration typically takes 30 seconds to 3 minutes, depending on the model and valve resistance. During calibration, do nothing – do not touch the head, do not press buttons, do not disconnect power. Simply wait until the display shows the current temperature or a completion confirmation. Interference with the process can cause incorrect recording of the stroke and the need to repeat calibration.

The head after calibration shows a different temperature than actual – is it a fault?

No, it usually is not. The sensor in the head measures the temperature in the immediate vicinity of the radiator, which is higher than the temperature in the center of the room. A difference of 1–4 °C is completely normal. The solution is to set a temperature offset (correction) in the head's menu according to a reference thermometer placed in the center of the room. If the difference is more than 5 °C, check whether the radiator is covered by furniture or curtains.

Do I need to repeat calibration after battery replacement?

It depends on the model. Most modern heads store calibration data in non-volatile memory (EEPROM), which does not require power. In such cases, calibration does not run after battery replacement and does not need to run. Some older or cheaper models, however, initiate calibration on every power-up. Check in the manual whether your model repeats calibration after battery replacement or not. If after battery replacement the actuator starts moving in a characteristic way and the display shows "CAL", calibration is running automatically – this is normal.

What to do if calibration ends with an error (error on the display)?

An error in calibration usually means that the actuator could not find one or both stops. First steps: check that the adapter is correctly mounted and tightened, check that the valve is not mechanically blocked (stuck due to corrosion), insert new batteries, and repeat the calibration. If the error persists, try manually pressing the valve stem (with the head removed) – if the stem does not move or is very stiff, the valve insert needs to be replaced. More tips for diagnostics can be found in the article Programmable head does not heat or close – common faults and solutions.

Is it possible to completely disable calibration and set the stroke manually?

For most common programmable heads on the market, it is not possible to set the stroke manually – automatic calibration is the only way. Manual stroke setting is more of a feature of industrial or specialized actuators for HVAC systems. If you have a non-standard valve with an extreme stroke, contact the manufacturer's technical support – some models have in the service menu the option to correct the calibrated range.

After calibration, the head opens the valve, but the radiator does not heat – why?

This is a question that does not relate to calibration itself, but to the environment. Check: (1) whether the boiler is on and actually supplying hot water, (2) whether the shut-off valve under the radiator is not closed, (3) whether the radiator is not bled – air in the radiator prevents circulation and the radiator remains cold despite an open head, (4) whether the system pressure is not too low (check the manometer on the boiler). The programmable head itself only controls the water flow through the valve – if hot water is not coming, the problem lies elsewhere in the system.

Conclusion

Calibration and adaptation of a programmable head are not complicated processes, but they require a systematic approach and a bit of patience. Most of the problems customers complain about – inaccurate temperature, the head does not heat, the radiator does not warm up – have their roots precisely in an inadequately performed calibration, incorrect sensor offset, or a mechanical issue with the valve that only becomes apparent during a functional test. If you take the time after installation to systematically verify – mechanical test of opening and closing, setting the offset according to a reference thermometer, checking hysteresis and protective functions – you will save yourself a lot of frustration in the following months.

The full range of programmable heads can be found on the atria.sk website, including detailed technical data sheets and instructions for individual models. When choosing a specific model, also read the article Frequently asked questions about programmable heads, where further practical information from customer practice is summarized.

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