My radiator valve is broken.

My thermostatic radiator valve snapped off

It is quite a common to find that a radiator valve is broken and as long as the valve isn’t leaking it is luckily pretty easy to fix.

Thermostatic radiator valve snapped off from the body
Thermostatic radiator valve snapped off

What are thermostatic radiator valves

Thermostatic radiator valves (abbreviated to TRVs) are designed to allow a property to have different temperatures in room depending on your preference.

How do they work?

Inside the plastic head is a capsule that expands as it gets hotter. This pushes a pin down onto the metal valve closing it as the room warms up. The head can be adjusted to control the temperature of the room.

They come in two pieces. The shiny silver coloured metal valve holds the water from the central heating system and the plastic head controls the valve according to the air temperature around it.

Are radiator valves universal?

Radiator valves are made by several different companies and are unfortunately not universal and not all the same size. This only applies to the plastic thermostatic head that sits on top and the connection to this head.

Radiator valve pipe sizes

The pipes that go into the valve are universal sizes (in the UK). The pipework comes in the following sizes:

  • 15mm
  • 10mm
  • 8mm

This can be in copper, chrome copper, or in a variety of plastics. The material may be different but the size will be the same.

Radiator valve tails

The connection from the radiator valve to the radiator itself (known as the tail) also comes in two sizes.

The more modern type are 1/2 inch threaded to 15mm compression.

The older (but still available) type are 1/2 inch threaded to a 3/4 inch joint.

Radiator valve joint to the radiator

Almost all radiators now come with a 1/2 inch threaded joint to allow the installation of the radiator tail.

Some older radiators have a 3/4 fitting which would require a different size tail and probably a different size valve.


Radiator valves are not all the same size due to the different manufacturing methods of the companies that make them. They all believe their design is the best so they carry on making them. The pipe sizes are out of their control so they have to keep to those sizes.

Why has my thermostatic radiator valve snapped off?

The plastic connection that holds the head onto the metal valve is fragile and gets more fragile as the plastic ages. The slightest knock can shatter the plastic and cause the valve head to fall off.

In most modern designs the head is held onto the valve with a metal screw ring.

Once the head is pushed onto the body it is secured by tightening this screw ring.

Can I change a TRV myself?

If a radiator valve is broken you can change them yourself. Just changing the head doesn’t involve any plumbing. However there are two complications when changing a TRV head.

  1. Some brands of TRV heads aren’t compatible with other brands.
  2. The inner workings of the metal valve may be stuck or broken.

In general a property will have all the valves the same so if one breaks you can look at the others to assess which type it is.

Different types of TRV head

The main brands are as follows:

Drayton – They have a pin in the valve body that is quite long and has flat sides. There are several designs of head but they are all compatible with the body.

A Drayton TRV 4 TRV head. A replacement if you thermostatic radiator valve snapped off
Drayton TRV4 head

A Drayton thermostatic radiator valve
Drayton RT212 TRV head

Pegler / Terrier

The valves are recognisable by the pin being flatter, wider and has slanted sides.

A Pegler Terrier thermostatic radiator valve
Pegler terrier TRV head

Myson – they have a tall thin flat sided pin in the valve much like the Drayton valves. Drayton and myson valves aren’t compatible they may screw on but they won’t work.

myson TRV1 thermostatic radiator valve
Myson TRV head

What to do next

I would recommend going to the amazon page for thermostatic radiator heads and matching the broken head to the picture on amazon.

This is the link to the amazon page for thermostatic radiator valves.

Visually match your broken valve with the one on the web page.

If you don’t have the broken head most of the valves in your house will be the same type so you can assume it’s the same.

When it arrives turn the new head so it is on the maximum temperature (fully open) push it into place then screw the ring onto the thread.

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