Thermostatic radiator heads: how to choose, set and replace them

In short: a thermostatic head can be changed in a few minutes, without draining the heating system. The key is to choose a head that is compatible with the valve body: most valves have an M30 x 1.5 thread, but Danfoss valves and a few other brands need a specific head or an adapter. Set to 3, a thermostatic head keeps the room at about 20 °C.

How does a thermostatic head work?

A thermostatic valve has two parts: the valve body, fitted on the radiator's flow pipe, and the thermostatic head, the graduated knob you turn by hand. The head contains a sensor filled with liquid, wax or gas that expands as the room warms up. As it expands, it presses on a small pin in the valve body, the valve pin, and reduces the flow of hot water. When the room cools down, the valve opens again.

So the head does not control the radiator's temperature, but the room's. Turning the head to 5 does not heat faster: the radiator simply shuts off later, at a higher temperature.

What do the numbers 1 to 5 mean?

Each number corresponds to an approximate room temperature. The values vary slightly between manufacturers, but setting 3 gives about 20 °C on most of them:

Between two numbers, the small marks are worth about 1 °C. Some heads also have a zero position (0) that closes the valve completely, without frost protection.

Getting the settings right every day

• Aim for about 20 °C in living areas. In bedrooms, 17 to 18 °C is usually enough. According to the Swiss Federal Office of Energy, each extra degree increases heating costs by 6 to 10%.
• Set all the heads in the same room to the same setting, otherwise one radiator works for the other.
• When airing the room, turn the head to the snowflake for the few minutes the window is wide open: otherwise the valve opens fully as soon as the cold air comes in.
• Keep the head unobstructed: a curtain, a piece of furniture or a radiator cover creates a pocket of heat and the head closes too early.
• Most heads let you limit or lock the setting range with small clips, which is handy in a child's room or a shared space.

Choosing a head that fits your valve

This is the most important step. Before buying, look for the brand marked on the valve body, or remove the old head to see the type of fitting.

• M30 x 1.5 valve: IMI Heimeier K, Oventrop Uni LH, Danfoss React M30 x 1.5 or Evenes Standard.
• Danfoss RA valve: Danfoss Aero RA Click or Danfoss React RA Click.
• Danfoss RAV or RAVL, Herz or Vaillant valve: IMI Heimeier heads with direct connection for Danfoss RAV, Danfoss RAVL, Herz and Vaillant.
• An M30 x 1.5 head on another brand of valve: the IMI Heimeier adapter is available for Danfoss RA, RAV and RAVL, Herz, Comap, TA, Vaillant, Giacomini and older Oventrop valves (not for radiators with built-in valves).

Which type of head should you choose?

• Standard head with built-in sensor: the most common case, when the head is unobstructed and mounted horizontally.
• Head with remote sensor or remote control: essential if the head is hidden behind a curtain or radiator cover, sits in a narrow recess or is mounted vertically. The sensor is then placed away from the radiator, where it really measures the room air. Examples: IMI Heimeier K with 2 m remote sensor, IMI Heimeier F with remote control.
• Design head: same operation, refined finish, for example the 2TT head in chrome or white.
• Public-building or anti-theft version: for schools, offices, corridors and rental buildings. The setting range is limited and the head is protected against removal. Examples: IMI Heimeier B, Danfoss Aveo public-building version.
• Programmable electronic head: it automatically lowers the temperature at night or while you are away. Examples: Danfoss Eco 2, Resideo THERA Pro HR90 or the IMI Heimeier HeimSync connected head. Check compatibility with your valve on the product page.

Replacing a thermostatic head, step by step

No need to drain the system or switch off the heating: the head is not in contact with the water. The valve body stays in place and watertight.

1. Turn the old head to 5. In the maximum position, it barely presses on the valve pin and is easier to remove.
2. Release the fitting: for a screw-on head, turn the nut anticlockwise, by hand or with water pump pliers, protecting the nut with a cloth. For a Danfoss RA head, loosen the ring or press the release button, depending on the model. Remove the head.
3. Check the valve pin. Press it with your finger: it should go in a few millimetres and spring back on its own. If it is stuck, which often happens after the summer, gently work it free with pliers, without forcing. If it stays stuck or water seeps around it, the valve insert must be replaced: leave this job to a heating engineer.
4. Turn the new head to 5, place it on the valve body with the scale clearly visible, screw the nut on by hand, then tighten slightly. No sealant is needed.
5. Set the temperature you want, for example 3, and wait a few hours before judging the result.

When should you replace a thermostatic head?

• The radiator stays cold whatever the setting. Check the valve pin first (see above): it is often the culprit, not the head.
• The radiator heats all the time, even on the snowflake setting.
• The head is cracked, stiff to turn or its scale is unreadable.
• The room never reaches the chosen temperature, or clearly exceeds it.

If the radiator is warm at the bottom but cold at the top, the head is not to blame: there is air in it. See our guide Bleeding a radiator: when and how to do it.

Frequently asked questions

Do you need to drain the heating to change a thermostatic head?

No. The head fits onto the valve body, which stays watertight. Only replacing the valve body itself requires draining, at least partially.

Can you fit a head from another brand on your valve?

Yes, if the fitting is the same: an M30 x 1.5 head fits all M30 x 1.5 valves, whatever the brand. For a different fitting, choose a dedicated head or add an adapter.

What should you do with thermostatic heads in summer?

Leave them open, on 5. The valve pin stays free and is less likely to stick during the months without heating.

Does setting the head to 5 heat the room faster?

No. As long as the room is cold, the valve is open just as much on 3 as on 5. On 5, the radiator simply shuts off later, and the room ends up too warm.

Does an electronic head really save energy?

It automatically lowers the temperature at night and while you are away, without you having to think about it. The saving depends on your habits: if you already turn your heads down by hand, it will be smaller.

Find the right thermostatic head

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