This is quite a common problem and is luckily pretty easy to fix.
Thermostatic radiator valves (abbreviated to TRVs) 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.
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.
There are two complications when changing a TRV head.
- Some brands of TRV heads aren’t compatible with other brands.
- The inner workings of the valve may be stuck.
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.
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.
The valves are recognisable by the pin being flatter, wider and has a slanted sides.
Myson – they have a tall thin flat sided pin in the valve much like the Drayton valves.