What is a thermostatic valve?
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Stefano Fonseca is an energy and environment engineer with over six years of experience in technical building equipment (TGA). He combines technical expertise with a passion for understandable communication. For more than five years, he has been writing as a freelance editor about renewable energy and sustainable living, in particular about photovoltaics and heat pumps.
Small rotation, big effect: Anyone who has ever turned on the radiator is familiar with the thermostatic valve — often overlooked, but decisive for living comfort. But what exactly is behind this inconspicuous component that regulates heat without you thinking much about it? You can find out here.
What is a thermostatic valve?
A thermostatic valve is a temperature controller on the radiator that automatically adjusts the flow of heating water to the room temperature. It consists of a thermostatic head and a valve base. If the room temperature rises, the valve partially or completely closes the heating water flow, if it drops, it opens again. This keeps the desired room temperature constant and saves energy.
How does a thermostatic valve work?
A heating valve automatically regulates the heating water supply to the radiator. Inside the valve, there is a temperature sensor with an expandable medium (such as wax or liquid) that expands or contracts depending on room temperature. When the temperature rises, the medium pushes a pin inwards, which closes the valve and reduces the flow of hot water. If the temperature drops, the medium contracts, the valve opens again and the radiator becomes warmer.
There are various types of thermostatic valves — mechanical, electronic and smart — which differ primarily in their way of temperature regulation and control.
Where is a thermostatic valve installed?
A thermostatic valve is installed directly on the radiator, usually at the upper side connection point. There, it controls the amount of heating water flowing through and thus the heat output of the radiator. In modern heating systems, the thermostatic valve is an integral part of every heating surface; in older systems, it can be retrofitted. The positioning enables precise temperature control, as the valve measures the room temperature in the immediate vicinity.
Can a thermostatic valve break?
A radiator valve may break. Typical signs are radiators that remain cold despite the setting turned on or heat permanently even though the room is already warm. The causes are often calcified or stuck valve pins, defective temperature sensors or mechanical wear inside the valve. In such cases, the thermostatic valve should be checked and replaced if necessary.
Is the thermostat calcified or clogged?
You can tell whether a thermostatic valve is calcified or clogged by a stuck valve pin or by the fact that the radiator remains cold. In this case, lime or dirt may have settled in the valve. The valve pin can often be carefully released with slight pressure. If the problem persists, you should have the valve checked or replaced by a specialist.
When should you replace a thermostatic valve?
A thermostatic valve should be replaced if it no longer regulates correctly, the radiator remains cold despite the setting turned on, or the valve is stuck. It is also recommended to replace very old models over 15 years of age. This allows you to reduce heating costs and increase comfort.
How to replace a radiator valve:
- Switch off the heating system and wait for the radiator to cool down.
- The old thermostatic head by turning or loosening the attachment (usually a screw nut) removing.
- With your hand or with pliers Check valve position and determine whether the valve pin is easy to push in. If it is tight, remove it carefully if necessary.
- Den new thermostat head correctly on the valve Put on and fix. Make sure that it is oriented horizontally.
- Switch the heating back on and check whether the radiator gets warm when the temperature is set.
- Perform functional testing by you dSet the thermostat to a low level and see if the radiator cools down. Then turn it back on.
Adjusting the thermostat valve: How to do it correctly
The correct adjustment of the thermostatic valve saves energy and ensures a pleasant indoor climate. The numbers on the rotary head represent fixed temperature ranges — anyone who understands them and uses them in a targeted manner can improve heating comfort and reduce heating costs. The following is a checklist.
How much does a thermostatic valve cost?
A simple mechanical thermostatic valve costs from around 10 euros, while electronic or smart models range between 30 and 100 euros, depending on the equipment. For professional exchange by a specialist company, an additional 50 to 100 euros per radiator is required.
What do the numbers and symbols on the thermostatic valve mean?
The numbers on the thermostatic valve represent fixed temperature ranges:
In addition, there are symbols with fixed meanings:
- star or snowflake = Frost protection (approx. 6—8 °C)
- sun = default setting (approx. 20 °C)
- crescent = reduction at night (approx. 14 °C)
How do I lay out thermostatic valves?
It is best to install thermostatic valves as part of a hydraulic balancing off. Experts determine the heat requirement of each room and the required heating water flow rate. This is the only way to optimally adjust the valves to the heating output of the system.
The correct pressure loss is particularly important. If it is too low, the valve works imprecisely or stops in intermediate positions. If the pressure drop is too high, the pump's power consumption increases. Three characteristic values help to select the valves:
- Rule difference: Indicates when the valve deviates completely from the set temperature.
- Kv value: Shows how much water flows through the valve at a certain pressure. It determines the flow rate.
- valve authority: Describes the ratio of the pressure loss of the valve to the pressure loss of the entire system and should be between 30 and 70 percent.
A correctly designed thermostatic valve ensures even heat distribution, reduces heating costs and increases the energy efficiency of the entire system.
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