Whether your home heating is powered by a gas boiler, a heat pump, an electric boiler or something else altogether, it’s likely that you’ll still have radiators. Radiators are the main way in which heat can be injected into our homes, as well as underfloor heating, so even in the future, it is likely they’ll continue to be a staple.

To control the flow of water, and therefore the heat output, most radiators have valves, also known as thermostatic radiator valves (TRVs). Below, you can find out more about how these work, the different types and what the symbols on them mean.

What is a thermostatic radiator valve?

When you look at your radiator head on, you’ll see a valve on either side of the radiator. One usually has a small plastic cap on the top, and this is the one that controls how much water can flow into the radiator. This is known as the lockshield valve and cannot be easily altered. When your radiator system was initially installed, it’s likely that the heating engineer adjusted this to the correct setting for the water to run through the system evenly. It’s this valve that is used to balance your radiators.

The valve on the opposite side is the radiator valve, which controls the temperature, much like a tap can be turned to change the flow of water. There are two types of radiator valves: thermostatic and manual.

What’s the difference between a manual TRV and smart TRV?

A manual radiator valve can be controlled and turned by you to the temperature you want, just like a tap. Turn it one way to increase the temperature, and the other way to cool the radiator down. Once the room has reached the right temperature, you can manually turn the valve back down.

A thermostatic valve works in a slightly different way and is a bit more clever in how it controls the room’s temperature. It has additional features so that it can sense the temperature of the room and adjust its heat accordingly.

They’re usually labelled with numbers, and the number three setting should result in an overall room temperature of 20 °C. However, if you want a room hotter or colder than this, you can adjust the valve, and therefore the temperature, accordingly. The higher the number, the hotter the temperature of the radiator, so number five is the hottest setting.

For the most part, this means that you should set the valve to a medium setting, such as number three, and leave it there. The radiator will do the rest, heating the room to the required temperature and cooling off slightly to maintain this temperature. This is better for your heating bills and energy consumption, as it means every room is only heated as much as it needs, rather than overheating. There is greater control over the temperature of the room. 

Some TRVs have digital displays that show the room temperature, whereas some will look very similar to manual valves. For this reason, TRVs shouldn’t be installed in the same room as a mounted room thermostat. This is because they’ll compete and could end up overheating or underheating a space. This may be why a smart room thermostat is better located away from radiators in a hall or similar space.

TRV with digital display

Some TRVs have digital displays that show the room temperature, whereas some will look very similar to manual valves. For this reason, TRVs shouldn’t be installed in the same room as a mounted room thermostat. This is because they’ll compete and could end up overheating or underheating a space. This may be why a smart room thermostat is better located away from radiators in a hall or similar space.

Do all radiators have thermostatic valves?

Building Regulations state that every radiator that’s part of a wet central heating system must have a TRV, apart from those located in the same area as a room thermostat. This means that electric radiators don’t need a TRV, as they work using electricity currents and not water, but your standard radiators will need a TRV.

What is a smart TRV?

Smart heating systems are much more commonplace now than they were a few years ago. With a smart thermostat, you can control your heating from your phone or another device, either remotely or while at home. This means you can turn your boiler on even when you’re not at home and return to a pre-warmed environment.

But you can take these systems one step further and introduce smart TRVs, too. This means you could ultimately control every radiator individually from your phone, choosing certain temperatures or settings for certain rooms. Generally, your bedroom should be slightly cooler than other living spaces, such as a lounge, so you could achieve this via your smart TRVs.

How do TRVs work?

A valve often opens or closes to perform certain tasks. When you open the valve on a tap using the handle, the water is allowed to flow. When the valve is closed, the water stops. TRVs work in a very similar way, but use temperature to control this opening and closing motion.

When metal gets hot, it expands. The valve contains a pin so that when it expands or contracts, the position of this pin is adjusted. When a room becomes too hot, expansion causes the pin to close, reducing the flow of hot water into the radiator. As the room cools down, contraction causes the pin to open so that more hot water can enter the radiator.

With a manual radiator valve, the physical turning of the valve opens and closes it, so these don’t contain a pin that relies on heat to move.

What do the symbols on radiator valves mean?

TRVs usually have a number system from 1 to 5, the former being the coldest setting and the latter being the warmest. There may also be a snowflake symbol on the valve, which is usually set to 5 °C and pretty much means the radiator is off altogether.

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