how to choose the correct pressure gauge range for your heating system

Choosing the correct pressure gauge range is a key factor for accurate pressure monitoring and safe operation of your heating system, as a poor choice can lead to incorrect assessment of the system's condition or premature wear of the device. In typical households, we most often encounter pressures in the range of 1 to 2.5 bar during boiler operation, but in professional systems or during tightness testing, the values can vary significantly. Therefore, it is necessary to choose a range in which the normal operating value falls into the middle third of the scale, which ensures maximum accuracy and long life of the measuring element.

Difference between normal and actual operating pressure

Many heating owners believe that it is sufficient to measure the current pressure and then buy a manometer accordingly, but they ignore the fact that the pressure in the system fluctuates depending on the water temperature and heating phase. In a cold system, the pressure is lower (usually 1.0 – 1.5 bar), but after heating to operating temperatures, it increases by approximately 0.3 – 0.5 bar, or even more in older systems without a properly functioning expansion vessel. If you have a manometer with a maximum range of only 4 bar, during normal operation the needle would be close to the upper limit, which increases the risk of mechanical damage to the spring and reduces the accuracy of the measurement.

• Normal operating pressure in a house: 1.0 to 2.0 bar (cold) to 2.5 bar (hot).
• Maximum allowable pressure for standard boilers: 3.0 bar, above which the safety valve is activated.
• Hydrostatic test pressure (test): Usually 1.5 times the operating pressure, i.e. around 4.5 – 6 bar.

The golden rule of positioning the working point

Experts recommend that the normal system operating pressure always lie in the middle or slightly below the middle of the entire manometer range, ideally in the interval between 25 % and 75 % of the maximum scale value. This principle stems from the physical properties of the Bourdon tube, which has the highest linear accuracy precisely in this area and minimizes the influence of friction and hysteresis at the ends of the scale. A manometer with a range of 0 – 10 bar is therefore often suitable even for smaller systems if you expect pressure surges, while a manometer with a range of 0 – 4 bar is optimal only for very stable low-pressure systems where no tightness test is expected.

When to choose a higher range and when a lower one

The choice between a manometer with a range of 0 – 4 bar, 0 – 6 bar or 0 – 10 bar primarily depends on the type of system and its use. For standard apartment heating with modern condensing boilers that have integrated expansion vessels and safety valves set at 3 bar, a manometer with a range of 0 – 6 bar is often sufficient and clear, leaving enough room for sudden pressure increases during air venting. On the other hand, in older systems or for professional maintenance technicians who need to measure test pressure for tightness, it is essential to use a manometer with a larger range, for example 0 – 10 bar, to avoid damaging the device during pressure tests.

On the other hand, if you are working with low-pressure systems, such as some types of floor heating with limited pressure, a more specific manometer of 0 – 4 bar may be advantageous, offering better readability of small changes. However, it is important to realize that when using this type of manometer, you must be certain that the system never exceeds 3 bar, otherwise there is a risk of permanent damage to the spring and measurement uncertainty. For standard boiler installation, the safest choice is therefore often a universal model with a range of 0 – 10 bar, which covers all common situations including hydrostatic testing.

Technical parameters and resistance to vibrations

An important aspect when choosing a range is also the internal construction of the manometer and its resistance to vibrations, which are common when working with gas boilers or circulation pumps. Manometers with a smaller range (e.g. 0 – 4 bar) often have finer springs that are more sensitive to mechanical shocks and can lose calibration more quickly if exposed to strong vibrations. Therefore, in professional installation, it is often recommended to use manometers filled with glycerin, which not only dampen vibrations but also prevent condensation and corrosion inside the device, thus extending their lifespan.

When choosing an axial manometer with a range of 0 – 6 bar or 0 – 10 bar, also note the size of the dial, which affects readability. For standard home use, a diameter of 63 mm is sufficient, but for more distant placement or for the need to monitor small changes more precisely, a diameter of 100 mm is more suitable. A larger dial allows for dividing the scale into smaller units, which is critical when diagnosing problems, as pressure may change by only tenths of a bar. Therefore, choosing the correct range must go hand in hand with choosing the correct size and type of device construction.

Practical examples from real-life practice

In practice, we have encountered several situations where an incorrect range selection caused problems. One case was an apartment building where manometers with a range of 0 – 4 bar were installed, but during the winter season and with the connection of multiple heat sources, the pressure in the system exceeded 3.5 bar, which caused permanent deformation of the springs and the manometers began to show false low values. Another practical example shows that during gas replacement in a boiler and subsequent tightness testing at 4 bar, a standard cheap manometer with a range of 0 – 6 bar immediately showed the exact value, while one with a smaller range would have likely been damaged. Therefore, it is always better to choose a slightly larger range than to risk damaging the device.

For the average customer who wants to simply monitor the pressure in the boiler, we recommend a combination of reliability and cost. For example, the model Axial manometer 0 - 6 bar, 63 mm is an ideal compromise for most family homes, where the operating pressure does not exceed 2.5 bar. If, however, you have an older system or plan to perform your own tightness tests, a safer choice will be Axial manometer 0 - 10 bar, 63 mm, which will provide you with sufficient reserve and protection against overload. These models are designed to withstand normal operating conditions and at the same time provide accurate data even at higher pressures.

Visual calibration of the scale for different systems

The diagram illustrates how the relative position of the normal operating pressure (black line) changes depending on the selected pressure gauge range; with a 0-4 bar range, the system operates near the maximum limit, whereas with a 0-10 bar range, it remains within a safe central zone.

Margin of Safety and Pressure Testing

This diagram demonstrates the critical difference between operating pressure and test pressure (hydrostatic test), where the correct selection of range (0-10 bar) ensures that even in the case of a sudden pressure increase to 1.5 times the operating value, the needle remains within the measurable range without the risk of damaging the spring.

Effect of vibrations on measurement accuracy

The diagram illustrates the damping mechanism of vibrations through glycerin filling, which prevents needle oscillation and subsequent wear of components. This is crucial when selecting a pressure gauge with a larger range (0-10 bar) installed near circulation pumps or gas boilers.

Frequently asked questions

Why does the pressure gauge show zero even though there is pressure in the system?

This phenomenon is often caused by a clogged capillary or damage to the spring due to overloading the pressure gauge beyond its maximum range. If the gauge was exposed to a pressure higher than 1.5 times its maximum range, the spring may have deformed permanently and is no longer able to return to its original position.

How to set the pressure gauge after changing the gas in the boiler?

A pressure gauge cannot be "adjusted" in the traditional sense, as it is a passive measuring device; after changing the gas, it is sufficient to check that it shows the correct operating pressure after the system has warmed up. If it shows a different value than other measuring devices, it means it is faulty and needs to be replaced with a new calibrated model.

What is better: a pressure gauge with a thermometer or a separate thermometer?

A pressure gauge with a thermometer (thermomanometer) saves space on the pipe and is more affordable, but for precise diagnostics, it is often better to use a separate thermometer with a larger dial, which allows for better monitoring of temperature changes without interference from the pressure needle. Thermomanometers are suitable for routine checks, while separate thermometers are preferred for more complex maintenance tasks.

Conclusion

Selecting the correct pressure gauge range becomes a simpler task if you follow the basic rule that the normal operating pressure should be in the middle of the scale, thus preventing premature wear and ensuring measurement accuracy. There is no universal solution for every system, so it is always advisable to consider not only the current pressure but also potential pressure surges during tests or seasonal changes. The correct choice between models 0 – 4 bar, 0 – 6 bar, or 0 – 10 bar will determine whether you have a reliable companion for your heating system or just an ornamental accessory that will let you down in a critical moment.

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.