Replacing a thermostatic head or radiator valve: which fits (M30, Danfoss RA, RAVL), head or complete valve, and when it makes sense

Short answer: you can replace the thermostatic head (the part you turn) yourself without draining any water: unscrew or unclip the old head and fit the new one. The only thing that has to match is the connection: M30 × 1.5 (most valves from Heimeier, Oventrop, Honeywell, Comap, Caleffi), Danfoss RA (clip ring with 23 mm) or the older Danfoss RAVL or RAV (26 and 34 mm, only with an adapter). Replacing the valve body itself (the valve with the pin that the head presses on) means draining or freezing the system; that is work for an installer. A smart head pays off if you want to control rooms separately or keep bedrooms cold during the day: expect 5 to 15 per cent less gas, €80 to €90 per head.

Head or valve: what is actually broken?

Which connection does my valve have?

Unscrew the old head (usually a knurled ring anticlockwise, or a screw on the side) and look at the valve. If you see a thread of about 30 mm in diameter with a pin in the middle: M30 × 1.5, the European standard that every universal head fits. If you see a smooth collar with a groove and a clip ring: Danfoss RA (23 mm valve neck); smart heads are supplied with an RA adapter. If you see a thicker neck of 26 mm (RAVL) or 34 mm (RAV) on a valve from before 1995: only with a separate adapter, and then replacing the whole valve body is often the neater option. Giacomini (M30 × 1) and Herz (M28 × 1.5) use different threads; adapters are available. If in doubt, measure the outside diameter of the thread or send a photo.

Mechanical, electronic or smart

A A mechanical head (€10 to €30 from a DIY store or installer) controls to room temperature using a liquid or wax filling and has no batteries. An electronic head with its own clock and display runs a weekly programme per radiator, such as the Honeywell HR93 (€86.95). A smart head communicates with a central thermostat or hub and controls each room, together with the boiler.

Smart heads work best when they actually control the boiler too: the head in the bedroom calls for heat and the thermostat switches the boiler on, even if the living room is already warm. This is possible with EasyControl, evohome and tado. Standalone smart heads without a link to the boiler only close the radiator; they only save energy in rooms that would otherwise be heated unnecessarily. Which thermostat suits your boiler is explained in Which thermostat suits my boiler.

How to replace the head

1. Turn the old head to the highest setting; the pin is then furthest out and the head will not jam.
2. Undo the knurled ring (anticlockwise) or release the clip ring or locking screw, and pull the head straight off the valve.
3. Check the pin: press it in; it should spring back smoothly. If it is stuck, work it carefully with pliers; put a drop of penetrating oil on the pin, not into the valve.
4. Slide the new head (with an adapter if your valve is Danfoss RA) onto the valve and tighten the ring by hand; no tools needed.
5. For a smart head: insert the batteries, pair it with the app or hub and let the calibration run (the head finds the open and closed positions itself).

No water, no draining, five minutes per radiator. If valves have different sizes on different sides of the house (after a renovation), buy the adapters separately.

Replacing the valve body

If the valve leaks or the radiator stays warm while the pin moves freely, the valve body has to come out. That means draining the system to below the radiator (or freezing the pipe with a freeze kit), unscrewing the old valve from the radiator and the pipe, fitting a new valve with new couplings, then refilling, bleeding and repressurising. Choose a valve with M30 × 1.5 and presetting (for balancing) and replace the lockshield valve on the other side of the radiator at the same time. Instalpunt does not install; have a qualified local installer do this as a small job, see the installation service; combine it with a boiler service to share the call-out charge.

Frequently asked questions

Does every thermostatic head fit every radiator?

No, the head fits the valve, not the radiator. With M30 × 1.5 any universal head fits; with Danfoss RA you need the supplied adapter; with old RAVL and RAV valves a separate adapter.

How much do I save with smart radiator heads?

Five to fifteen per cent of gas, most in homes with many rooms that are currently heated along with the rest. In a well-insulated open-plan apartment, the gain is small.

My valve has a handwheel instead of a pin. Can a thermostatic head be fitted to it?

No. A manual valve has no thermostatic insert. If you want thermostatic control, the valve body has to be replaced with a thermostatic radiator valve.

Why is there an asterisk on the head?

That is the frost protection setting: the head opens at a room temperature of about 6 °C, even on the lowest setting. So in unused rooms, do not close the valves completely; set them to the asterisk.