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What is a thermostatic valve (TRV)?

Posted by Jaga - 13 July 2016 Tips & Advice

Looking at how TRVs work, the different types and how to correctly use them to manage temperature and save on energy bills.

One part of a heating system that often gets overlooked is the thermostatic valve and head. They are just simply the things that get stuck onto radiators which we bang our legs on. Without giving it a thought we turn them right up when we are cold or finally turn them down when we find ourselves having to sit in our underwear as the room is so hot. Valves are critical to controlling the temperature of your home and individual rooms, TVR’s along with a thermostat and can save you up to 40% on your energy bills according to independent research carried out at

Salford University’s Energy House. The valve regulates the amount of hot water that enters the radiator depending on the surrounding air temperature, the head, senses the temperature and adjusts accordingly.

How do TRVs work?

Each thermostatic radiator valve head (TRV Head) has a liquid material or wax filled cylinder, this then expands or contracts depending on the heat, in turn pushing or releasing pressure on the pin to allow more or less water through to the valve. It is important to note that the TRV does not control the boiler, it simply regulates the flow of water to each radiator it is connected to when there is demand for heat.


Different types of valves:

There are different types of valves; manual, thermostatic and in-line.

Manual valves are not thermostatic, they control the flow of water manually, when the head is open water flows into the radiator, when it is closed no water enters the valve so there is no heat generated through the radiator. This is a cheap and simple way of controlling individual radiators. Manual valves are usually used to simply turn radiators on or off while being used in conjunction with a room thermostat and an in-line valve.

Thermostatic radiator valves (TRVs) offer fine control over the temperature of each individual radiator. They are connected and work by sensing the air temperature around the head which opens and closes the flow of water to the valve, depending on whether the TRV senses that the room is hot or cold will release more or less water into your radiator and heat or cool the room. TRV’s typically have 5 settings plus a frost setting which prevents the pipes freezing on very cold days, they are:

  • 1 (12oC), increasing by 4oC per setting
  • 2 (16oC)
  • 3 (20oC)
  • 4 (24oC)
  • 5 which is typically 28oC

A TRV is the most efficient way of controlling each radiator and therefore your energy costs. According to research carried out by the government the average UK house cost £714 to heat in 2015, so the pay back from fitting TRV’s would be less than a year. Obviously a pinch of common sense needs to be used i.e. turning the TRV or thermostat up to maximum will not heat the room up any quicker, it is best to set the TRV head and leave it allowing the room to get up to a constant, comfortable temperature.


There are a large number of manufacturers and range of valves and heads available, some starting at plain and simple and still gets the job done to the more decorative to suit all aesthetical tastes. Infrared, radio controlled and digital TRV heads are also available for more advanced systems.

Whatever system and radiators you go for, ensure you give the controls some thought, discuss with your installer before the work gets underway to ensure you are fully satisfied.

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