Understanding how the valves on your radiators actually work is a subject that often causes confusion. However your valves do an important job in ensuring the correct amount of hot water flows in and out of your radiators - ultimately making sure that your room is at your desired temperature. In this article we'll take a look at the different types of radiator valve that exist, with an emphasis on the function of lockshield valves.
On the vast majority of central heating radiators, there are 3 types of valve that you will encounter, with 2 ever being used at one time.
1. Manual / Twist Valves
Becoming rarer and rarer on modern radiators, manual valves are still common on old radiators or homes that have not upgraded their central heating systems for a long time.
Generally located on the flow pipe, a manual or twist valve can be identified by a cap that is very easy to twist by hand. It also might have a double-ended arrow on the top of the cap with + and - minus signs, indicating how open or closed the valve is. The more open the valve is, the more hot water will be able to flow into the radiator each time you turn your central heating system on.
With all radiator valves, truing anticlockwise opens the valve, while turning it clockwise closes the valve.
2. Thermostatic Radiator Valves (TRV)
Increasingly common on modern radiators in new-build homes or those with upgraded heating systems, TRVs tend to be used instead of manual twist valves. They can be identified by a twistable chunky cap that usually contain a series of numbers from 0 - 5. Each number correlates to a certain temperature with 1 being the coldest and 5 being the hottest. Setting the valve to 0 means the valve is completely off (or closed) and the frost setting can be used to stop your pipes from freezing if you're away during cold weather.
Contrary to popular belief, thermostatic radiator valves do not directly control the temperature of the radiator. They actually work by detecting the temperature of the room around the rad and valve and react accordingly. If the temperature of the room drops below the desired temperature, the valve will open to allow more hot water into the radiator to maintain the temperature. Once the room reaches, or starts to exceed, the desired temperature, the valve will close again to keep the temperature stable. The best way to get a comfortable temperature while not wasting hot water or energy is to set your TRV to 2 or 3.
Thermostatic radiator valves are a great way of controlling the temperature in each room of your home, allowing you to use less energy heating rooms you don't use very often. Because of this flexibility, they tend to be preferred to the old manual twist valves where the valves are either on or off without the ability to react to the temperature in the room.
3. Lockshield valves
These types of valves are usually located at the other end (the return) to TRVs or manual valves. They can be identified by having a fixed cap on them that cannot easily be twisted by hand. You'll normally need to remove the cap and use a pair of grips or a screwdriver to adjust them. Indeed, the name 'lockshield' refers to the difficult-to-adjust cap that is there deliberately to 'shield' against the valve being turned accidentally, allowing it to remain in a 'locked' position.
Lockshiled valves have 2 main purposes that are vital to the efficient running of a central heating system
1. Maintaining a balanced heating system
The lockshield valve plays an important role in controlling the amount of water that is returned to the boiler and the amount of water that goes onto the next radiator in your system, also known as heating system balance. Correctly setting your lockshield valves ensures that your radiators and heating system are balanced and water is distributed evenly between all the rads in your home.
An unbalanced system means that not enough water flows into the radiators that are furthest away from your boiler, leaving radiators close to the boiler hot and radiators further away cold. This can usually be resolved by closing (turning clockwise) the lockshield valve on the radiator closest to the boiler and then opening it (turning anti-clockwise) by half a turn. You can then repeat this process on each radiator in your system and you'll notice the previously cold radiators will now get hot.
2. A means of draining your system
From time to time, you or a professional plumber will need to drain all the water out of your heating system in order to perform maintenance or a repair. For example, this could be to get rid of radiator sludge or to repair a leak.
On one of your radiators, (usually downstairs in a two-storey house), there will be a lockshield valve that looks slightly different from the rest of the lockshield valves in your home. This particular lockshield valve will contain a drain-off, that is specifically designed to open up to allow the water to be completely drained from your system. Typically a plumber will attach a hose to the drain off and run the escaping water outside into a drain.