Thermostatic valves automatically regulate the flow of hot water through each radiator based on the room's temperature. In other words, when a room reaches the target temperature, they reduce the flow and stop providing unnecessary heat. Furthermore, according to the IDAE, this system can save between 8% and 13% on energy, making it an attractive option for your wallet.

Thermostatic valves: what do they do and how can they help you save?

Whether mechanical or electronic, a thermostatic valve is a device installed at the water inlet of each radiator to automatically regulate its flow. Its function does not involve the boiler, but rather stops a radiator from continuing to emit heat once the room has reached the selected temperature.

Inside the thermostatic valve is an internal sensor (or thermostatic liquid) that reacts by expanding or contracting depending on the temperature of the air surrounding the radiator. Here is how it works:

1. In a cold room, the sensor contracts, the valve allows a greater flow of hot water and the radiator emits heat.
2. Once the target temperature is reached, the sensor expands, pushes the internal pin and progressively reduces or cuts off the water flow.
3. This prevents the room from overheating and reduces the heating system's overall thermal demand.

How much can you save with thermostatic valves?

Comfort is rarely synonymous with saving money. But in this case, it is. According to the Institute for the Diversification and Saving of Energy (IDAE), it is estimated that installing thermostatic radiator valves or programmable thermostats can achieve energy savings of between 8% and 13%.

It is important to clarify that this estimate refers to the energy consumed for heating and does not represent a direct, identical reduction in your total gas bill. The actual saving will also depend on other factors, such as the property's thermal insulation, local weather conditions, the type of boiler and the household's usage habits.

When can you save the most with a thermostatic valve?

The true savings of thermostatic gas valves are most evident in homes with distinct thermal imbalances:

• If some rooms get too hot: In homes where certain rooms reach excessively high temperatures before the rest, hot water continues to circulate unnecessarily. In these cases, the valve detects the actual air temperature and restricts the flow, diverting or reducing the thermal demand to the rest of the circuit.
• If there are rooms you rarely use: A guest bedroom or one that is only used occasionally does not need to be the same temperature as the living room. Setting a lower target temperature in these areas prevents you from wasting gas.
• If your home benefits from different heat gains: Sunlight shining through the windows, the presence of several people or heat generated from cooking all increase the ambient temperature. The thermostatic head takes advantage of these free heat gains and automatically shuts off the flow to the radiator.
• If you currently have manual valves: Upgrading from a manual valve to continuous, automatic regulation represents the most significant leap in efficiency, as it prevents you from accidentally leaving the heating on full blast.

Does a thermostatic valve work the same way as a normal valve?

No. A manual valve acts like a traditional tap: you choose when and how much to open it, and it will stay in that position until you deliberately change it again. On the other hand, a thermostatic valve reads the ambient temperature and autonomously modulates the flow.

Thermostatic valve and thermostatic head: they are not exactly the same thing

A thermostatic valve is a device whose system is made up of two distinct parts:

• Thermostatic valve:  the valve body is the metal part connected to the pipe that mechanically opens or closes the water flow.
• Thermostatic head: the plastic or electronic part with the graduated dial that houses the temperature sensor and operates the valve mechanism.

Please note! On some radiators, simply changing or installing a compatible head may be enough. On others, you will need to replace the entire manual valve. Compatibility depends on your existing valve. If you want to delve deeper into this, keep reading.

Can you put a thermostatic valve on any radiator?

You are in luck: the answer is yes for most homes, although the procedure varies depending on the installation:

• If you already have a TRV-compatible valve: If your current valves have a metal pin with a spring under the cap, you simply need to screw on a compatible head.
• If you have an old manual valve: If the valve is old, you will need to partially drain the heating circuit, remove the manual valve and replace it with a thermostatic one by installing the complete valve body.
• If you have communal heating: In collective systems, you must first check the compatibility of the installation and find out how individual consumption is metered.

Manual or smart thermostatic valve: what is the difference?

• Mechanical head: It works without batteries or electrical connections. You set the numbered dial to a specific position and the internal mechanism constantly regulates the water flow.
• Electronic head: A smart thermostatic valve features a battery-powered digital motor. It allows you to set exact temperatures, establish heating schedules by room, detect temperature drops and connect to your mobile phone for remote control.

How to use a thermostatic valve properly to save money

Adopting good habits will be essential for saving on heating:

1. Choose a temperature and let it work: Let the valve do its own thing; it doesn't need to be constantly adjusted.
2. Don't turn it to the maximum setting to heat up the room faster: Turning the head to the maximum setting does not increase the radiator's power or speed up how quickly the room heats up. The speed depends entirely on the temperature of the water being sent by the boiler.
3. Don't heat every room equally: Adjust the heating based on how each space is actually used.
4. Lower the temperature where you need less heat: In rooms that aren't actively used, select maintenance or frost protection settings to avoid unnecessary consumption.

What do the numbers on a thermostatic valve mean?

We've talked about turning the head to the maximum setting, referring to position 5, position 1... The numbered scale (usually from 0 to 5) is a common source of confusion. In reality, it represents ambient temperature ranges, not power levels.

It's true that there is no universal equivalent for all brands. Although they vary by manufacturer, a standard guide for mechanical models is usually:

• 0 / *: off or frost protection position (approx. 5°C–7°C).
• 1: sleeping or storage environment (approx. 12°C–14°C).
• 2: bedrooms or hallways (approx. 15°C–17°C).
• 3: frequently used main rooms (approx. 18°C–20°C).
• 4: areas requiring greater comfort or bathrooms (approx. 21°C–23°C).
• 5: maximum setting (approx. 25°C–28°C).

What temperature should you set for each room?

We gave you a rough idea in the previous section. The IDAE recommends keeping living areas at a temperature of 21°C during the day. However, it is advisable to set the target temperature between 17°C and 19°C in bedrooms to promote better sleep, while maintaining between 14°C and 15°C is sufficient for unoccupied rooms.

Remember that every additional degree of temperature increases energy consumption by approximately 7%.

Does turning off radiators actually save gas?

There is a common belief that turning off radiators always helps save gas, but this isn't strictly true. If you turn down the heating in rooms you aren't using, the boiler will have to work less to maintain the temperature.

However, turning off all radiators completely can prevent water from circulating properly through the system and cause nearby rooms to lose heat more quickly. That is why thermostatic valves are designed to regulate the amount of heat gradually, not to cut off the water supply abruptly.

Thermostatic valve and lockshield valve: which one should you adjust to save money?

It is very common to confuse these two components installed on the radiator:

• Thermostatic valve: located at the top of the radiator and used to regulate the daily room temperature.
• Lockshield valve: located at the bottom to allow water to exit. Its function is to adjust and balance the flow of water entering each radiator so that the entire heating circuit in the home receives heat evenly. It should not be used to regulate the temperature.

Thermostatic valve or thermostat: what is each one for?

Thermostatic valves and thermostats are two components that complement rather than compete with each other:

• Thermostat: measures the central temperature of the house (usually in the living room) and sends the overall command to turn the boiler on or off.
• Thermostatic valve: manages the local water flow in each radiator independently.

How to combine a thermostat and thermostatic valves

To avoid system interference, you should not install a thermostatic valve in the room where the main thermostat is located. If the valve in this room were to close after reaching its temperature before the thermostat turned off the boiler, the boiler would keep running without being able to deliver heat to that reference radiator.

Therefore, you should install thermostatic valves in all other rooms to independently modulate their temperature while the main thermostat keeps the heating active.

Do not cover the thermostatic valve with curtains or furniture

The sensor on the thermostatic head measures the temperature of the air around it. If you place radiator covers, bulky furniture or thick curtains over the head, it will create a warm microclimate. The sensor will detect that the room is already warm and close the valve prematurely, leaving the rest of the room cold.

What to do with thermostatic valves when you open the windows

Opening your windows for 5 to 10 minutes is enough to ventilate your home in winter. During this time, you should turn the valve to the off or frost protection position (* or 0). If you leave it open, the head will detect the cold draught and open the flow to the maximum, wasting gas. For their part, most electronic heads close automatically when they detect a sudden drop in temperature.

How to install thermostatic valves on radiators with manual valves

If you are considering installing a thermostatic valve on a radiator, there are two procedures:

• When changing the head is enough: If the valve body mounted on the radiator is already TRV-compatible, you simply need to remove the protective cap or old dial and screw the new head onto the thread.
• When the valve must be replaced: If you have a manual valve, you will need to partially drain the water circuit and install a complete thermostatic valve. In this case, we recommend using a professional installer.

How much does it cost to fit thermostatic valves on radiators?

The total cost of installing thermostatic valves in a home is not a flat rate. The final budget will vary depending on the number of radiators in your home, the type of technology you choose and, crucially, whether your current installation requires work on the heating circuit.

To understand the budget range you might be looking at, it is helpful to look at three different scenarios:

• Replacing the head only: if the radiators in your home already have a TRV-compatible valve body, the job is very quick and affordable. In this case, your expenses are limited to buying the heads you need and screwing them on yourself.
• Replacing the entire valve body and head: If your radiators have old manual valves, you cannot attach a head directly. In this case, the entire metal part must be replaced with a thermostatic valve. The cost increases because you will need to hire a professional installer.
• Installing electronic or smart heads: If you want digital control, your budget will depend on the price of the devices themselves. In addition to the number of smart heads, you will need to factor in whether your system requires a Wi-Fi bridge to link all the radiators to your mobile phone.

Before investing in valves, check that your radiators are working properly

1. Bleed the air: bleed your radiators at the start of the season to remove any air bubbles that prevent water from circulating.
2. Check the pressure: ensure the boiler pressure is correct according to the manufacturer's instructions and that the unit is in good condition.
3. Check for leaks and balance the system: make sure there are no drips and that all radiators heat up evenly.

How to calculate whether it is worth installing thermostatic valves

To estimate the payback period for your home, you can use a simple mathematical formula:

Estimated annual savings (€) = annual heating cost × estimated consumption reduction

Then,

Payback period = installation cost ÷ annual savings

Calculate how much you could save by regulating your radiators

According to the IDAE's SPAHOUSEC II statistical analysis of natural gas consumption in households, the average heating consumption of a home in Spain is 4,522 kWh/year, representing 57.1% of total gas usage. Based on the current price of Endesa's Gas Tariff at €0.0843/kWh (September 2026, excluding taxes and with discounts applied), we can determine that the average heating cost would be €381.20 per year. With this figure in mind, and knowing that the estimated reduction is between 8% and 13% according to the IDAE, we can proceed with the equation:

381.20 × 0.08 = €30.50/year in savings

381.20 × 0.13 = €49.56/year in savings

Now it is time to calculate the payback period to see if the installation is truly worth it. To do this, we will take the first scenario, where simply changing the thermostatic head is enough, and assume that a pack of 6 heads (for 6 radiators) costs around €30.

30 ÷ 30.50 = 0.98 years

30 ÷ 49.56 = 0.61 years

Conclusion: in this hypothetical example, an installation costing €30 would pay for itself in approximately 7 to 12 months, depending on the actual savings. Bear in mind that these savings are only an estimated average and therefore do not guarantee a direct reduction in your bill. More complex installations will require a greater investment and consequently take longer to pay for themselves, which will also depend on your consumption level and tariff price.

When thermostatic valves will probably save you less

The potential for savings could be reduced in the following scenarios:

• If the property is only occupied for a few hours a day and the heating is barely turned on.
• If the home's main issue is heat loss due to poor insulation in the windows or exterior walls.
• If all rooms are exactly the same size and have the same constant thermal needs.

Why is the radiator still hot even though you've turned down the thermostatic valve?

If you find that a radiator stays hot even with the valve closed, it could be due to:

• Thermal inertia: aluminium or cast iron radiators take time to cool down after the water flow has been cut off.
• Ambient temperature lower than the system setting: if the room is very cold, the valve will keep the flow open, even if you have turned the dial down to an intermediate position.
• Jammed mechanism: if the thermostatic valve won't close, the internal pin may be stuck due to limescale build-up. Removing the head and gently pressing the metal pin usually solves the problem.

Why is the radiator cold even though the valve is open?

If the radiator isn't heating up despite the head being open, it may be because:

• The room has already reached or exceeded the temperature set on the head.
• The thermostat has turned off the boiler.
• Air has built up at the top of the radiator (and it needs bleeding).
• The lockshield valve at the bottom is closed or restricted too tightly.

FAQs about thermostatic valves and saving gas

How much gas can you save with thermostatic valves?

The IDAE places the potential energy savings at between 8% and 13% for zoned regulation systems compared to manual installations.

Does a thermostatic valve turn off the radiator?

Yes, when the ambient temperature reaches the selected setting, it restricts or stops the flow of hot water. It automatically opens again when the room cools down.

Can I turn off the heating in rooms I don't use?

It is advisable to set a lower temperature, rather than turning them off abruptly, which can unbalance the system.

Do I need to put thermostatic valves on all my radiators?

They should be placed on all radiators, except in the room where the main thermostat is located.

Do they need electricity?

Traditional mechanical heads do not need power. Electronic or smart models are battery-powered.

Why does the radiator cool down even when the heating is on?

This is usually a sign that the thermostatic valve has done its job: the room has reached the desired temperature and the device has temporarily cut off the flow to avoid wasting gas.