The numbered control found on the side of your radiator may look inconspicuous, but it has a very important job. Commonly referred to as TRVs, thermostatic radiator valves are used to control the air temperature of different rooms in a house. The valve regulates the volume of water going into a radiator so that the radiator varies in temperature depending upon what number setting the valve is on and the temperature of the room. They are a great energy saver and well worth installing if you do not have one on your radiator already. However, thermostatic valves are prone to a couple of problems, the most common being that they can get stuck.

Why do thermostatic radiator valves stick?

The top of the valve consists of a wax capsule that is heat sensitive and, therefore, expands and contracts. As it swells and shrinks, it pushes down on a pin within the lower section of the valve body. The pin pushes down on the washer that regulates how much water flows through the valve and into the radiator.

In the summertime, when your central heating is turned off, the valve head or the wax capsule will become hot through the increased summer temperatures and will push down on the pin. The consistent warmer summer temperatures often mean the pin remains in the same position for the entire summer. When winter comes, it is not uncommon for the washer to be stuck within the valve, preventing the radiator heating up.

To prevent the TRV from sticking, the best thing to do at the end of the heating season would be to open the valve so that it is fully open. You can then turn the heating system off.

How to fix a stuck thermostatic valve

If the pin has stuck, you can take the valve head off and tap the centre pin very gently, which will release the washer, and the valve should work. It would not be advisable within any room to completely close the valve. Closing the valve fully is likely to encourage dampness into the room and, therefore, create mould, discolouration, and other health risks.

Other thermostatic valve
problems include


Avoid putting TRVs on radiators that are in the same room as the room thermostat.
It is possible to put a TRV on every single radiator in your house. However, it would be advisable to not put one on radiators within the room where the room thermostat is sited. This room is sensing the temperature and you want the temperature to rise and spread throughout the house. When the room temperature reaches the level you have selected on the room thermostat controls, it will then shut off all the radiators. Because the room thermostat controls the valve, that controls the whole of the central heating system.


Avoid putting TRVs inside radiator covers.
If you have got radiator covers, you should not place thermostatic valves inside the covers. The covers will trap a certain amount of heat, meaning you will get a higher temperature reading inside the cover than inside the room. Instead, consider purchasing a TRV that can protrude through the side of the cover. Depending on how your cover has been designed, it may be possible for you to have an external sensor (to ensure it senses heat outside the cover). External sensors are simply a very small rectangular box (approx. 5cm high and 1cm deep) that sit outside the radiator casing.

All in all, thermostatic radiator valves are great devices if you are looking for ways to save energy at home. For instance, let’s say you live in a large house over three floors. We all know heat rises, so you might find the top floor rooms getting too hot. In which instance, a thermostatic valve would mean you could turn the radiators in those rooms down to a very low setting. Then, if the room started to get a little chilly, the radiator would come on. Essentially, you will only be using heating energy when and where it is needed, rather than blasting out heat all over the house when you only need it in one or two rooms.

Malcolm Osmore
Managing Director at Maintracts Services

If you are unable to get your radiator working properly and prefer to leave the hard work to the professionals, you know where to find us. We’re here for all your radiator and heat control needs.