Price Match Promise
Free Delivery* | Easy Returns
Up to 25 Year Extended Guarantees
What is a lockshield radiator valve?
If you’ve ever looked down at a radiator and wondered what all those little valves do, you’re not alone. Radiator valves can be confusing, but they play a really important role in keeping your home warm, comfortable and energy efficient.
Among the most misunderstood is the lockshield valve. It doesn’t have a numbered dial or an obvious on/off control, yet it's a vital compenent that keeps your heating system balanced and running properly. In this article, we’ll explain what a lockshield valve is, how to identify it, why it’s important, and how it fits into the bigger picture of your home’s central heating system.
Table of Contents
The main types of radiator valve
Every radiator has two valves, one at each end, and together they control how much hot water flows in and out of the radiator. The three main types you’re likely to come across are manual valves, thermostatic radiator valves (TRVs), and lockshield valves.
Manual valves
Manual valves are the simplest type, and they’re exactly what they sound like, valves you turn by hand to control how much hot water enters your radiator. They’re often found on older systems or radiators that haven’t been upgraded for a while. You can recognise them by their small twist cap, sometimes marked with “+” and “–” symbols to show whether you’re opening or closing the flow.
Turning the cap anticlockwise opens the valve to let more hot water in, while turning it clockwise closes it off. They’re perfectly functional, but they don’t offer any automation or temperature control, which is why most modern homes have moved on to thermostatic versions.
- Further reading: How Do Radiator Valves Work? A Complete Guide
Thermostatic radiator valves (TRVs)
Thermostatic radiator valves are now the standard in most modern heating systems and new-build homes. They look chunkier than manual valves and usually have a numbered dial ranging from 0 to 5. These numbers correspond to approximate room temperatures, with 0 being off, 1 being cool, and 5 being warmest.
Unlike manual valves, TRVs don’t control the temperature of the radiator directly. Instead, they sense the temperature of the room around them and adjust automatically. If the room cools down below the set level, the valve opens to let more hot water in. Once the room warms up, it closes again to maintain a steady, comfortable temperature.
This makes them far more energy-efficient, as you can set different temperatures in different rooms rather than heating the whole house to the same level.
- Further reading: The Best Thermostatic Radiator Valves
Lockshield valves
The lockshield valve is usually fitted to the opposite end of the radiator from the TRV or manual valve. It doesn’t have a visible control dial and often looks like a plain plastic or metal cap. You can’t easily turn it by hand, which is actually the point.
The “lockshield” name refers to the protective cap that shields the valve from accidental adjustments. Underneath that cap is a small metal stem that can be turned using a spanner or screwdriver. The lockshield valve controls how much water leaves the radiator and flows back into the boiler.
By carefully setting how open each lockshield valve is, you can make sure every radiator in your system receives the right share of hot water, keeping your heating balanced and efficient.
- Further reading: Does it Matter Which Side of the Radiator Flows and Returns?
What does a lockshield valve do?
The lockshield valve is sometimes considered as the 'balancing valve' because its job is to ensure each radiator in your home receives the right amount of hot water. Without it, the radiators closest to the boiler would heat up very quickly while those further away might struggle to get warm.
By slightly restricting the flow through the radiators nearest the boiler, the lockshield valve allows hot water to circulate more evenly throughout the system. When correctly adjusted, your heating will warm all rooms consistently, operate more efficiently to save energy and money and place less strain on your boiler and pump.
How to identify your lockshield valve
You’ll usually find the lockshield valve on the opposite end of your radiator from the manual or thermostatic valve. It’s easy to recognise once you know what to look for.
The cap is small and plain, often white or metallic and it doesn’t have any numbers, symbols or temperature markings on top. Unlike a thermostatic or manual valve, it won’t twist easily by hand. To adjust it, you’ll usually need to remove the plastic cap to reveal the small metal valve stem beneath, which can then be turned gently with a spanner or screwdriver.
The name 'lockshield' comes from the protective cap, which shields the valve from accidental knocks or tampering and keeps it locked securely in position once it’s been set correctly.
Balancing your system
Balancing is one of those behind-the-scenes jobs that makes a massive difference to comfort and efficiency but is rarely talked about.
A balanced heating system means that every radiator gets the right share of hot water, regardless of its distance from the boiler. If your home has radiators that heat up much faster than others, or one that stays stubbornly cold, the system may be unbalanced. Your lockshield valves are often the key to putting that right.
It is possible to ajust your lockshield valves and balance your system yourself, but it needs care and patience. The goal is to slightly reduce flow through the radiators closest to the boiler and allow more to reach the ones further away. If your system is large, old or uses complex pipework, balancing can become tricky. In that case, it’s worth calling a professional heating engineer who can use temperature readings to set them precisely.
- Further reading: How to Balance a Radiator - A Complete Guide
Draining your system
Many homeowners assume that the lockshield valve itself is used to drain the system. In reality, the job of draining belongs to a small fitting called a drain-off cock (or drain valve).
You’ll often find a drain-off fitted to one of the lockshield valves, usually on a downstairs radiator. It looks like a little tap or nozzle and is designed so a hose can be attached to it. When opened, it allows all the water in your heating system to be safely drained out such when replacing a radiator or removing sludge.
So while the lockshield controls flow balance, the drain-off allows maintenance and emptying of the system.
- Further reading: How to Drain a Central Heating System
Radiator valves from TradeRadiators.com
The lockshield valve might not be as visible or as flashy as a thermostatic valve, but it’s essential for keeping your central heating system running efficiently. By carefully controlling the return flow of water, it ensures every radiator in your home heats up evenly, your boiler doesn’t work overtime, and you enjoy consistent warmth in every room. If you’ve been wondering why some of your radiators are cooler than others, a well-adjusted lockshield valve might be the answer.
If your current valves have seen better days, or you’re upgrading your heating system, take a look at the huge range of radiator valves available at Trade Radiators.
We stock everything from sleek modern TRVs to classic brass manual sets, all supplied in pairs (TRV and lockshield) to make installation simple. With free delivery to most of the UK mainland, you’ll find high-quality valves to suit every radiator, style and budget.
