What are radiator valves and how to choose the correct one?
What Are Radiator Valves?
Radiator valves are the fittings that connect your radiator to your central heating system's pipework. They sit at the base of the radiator — typically one on each side — and their primary job is to control the flow of hot water entering and leaving the radiator. In doing so, they directly determine how much heat a radiator produces in any given room.
Think of them as the tap for your radiator. Open the valve fully and the radiator gets maximum hot water flow, producing maximum heat. Close it down and the room stays cooler. Without valves, you'd have no way to adjust individual radiators at all — every room in your home would receive the same amount of heat regardless of need.
Beyond basic heat control, radiator valves also play an important role in system efficiency and maintenance. They allow individual radiators to be isolated and removed without draining the entire heating system, making repairs and replacements significantly easier and less disruptive.
Types of Radiator Valves
Manual Radiator Valves
Manual valves are the simplest and most affordable type. You turn them by hand — usually via a cap or a knob — to open or close the flow of water. They have no automatic mechanism; once you set them to a position, they stay there until you change them again.
They're reliable, long-lasting, and require no batteries or programming. The trade-off is that they offer no automation whatsoever. If you leave the house and forget to turn down a radiator, it will keep heating that room all day. Manual valves suit rooms where you want consistent, unchanging heat, such as a hallway or utility room, and they're ideal for people who prefer simplicity over smart features.
Thermostatic Radiator Valves (TRVs)
TRVs are by far the most popular type of radiator valve in UK and European homes today. They contain a wax or liquid element inside the valve head that expands or contracts in response to the room's air temperature. As the room warms up, the element expands, gradually closing the valve and reducing the flow of hot water. When the room cools down, it contracts and reopens the valve. The result is an automatic, self-regulating system that maintains a set temperature without any intervention from you.
Most TRV heads feature a numbered dial, typically from 1 to 5, where each number corresponds to a rough temperature range. Setting a TRV to 3, for example, generally keeps a room around 20°C, though this varies slightly between manufacturers.
TRVs are strongly recommended by energy experts because they prevent overheating and reduce wasted energy room by room. They cannot, however, be used on the radiator in the same room as your main thermostat, as both devices would compete to control the boiler.
Lockshield Valves
Every radiator in your home also has a lockshield valve, usually found on the opposite side from the control valve. These are not designed for regular adjustment by the homeowner — they come with a plastic cap that must be removed with pliers to access the adjustment point underneath. Lockshield valves are set by a heating engineer during a process called balancing, where each radiator in the system is fine-tuned to receive the correct proportion of hot water. This ensures radiators further from the boiler heat up just as effectively as those closer to it. Once set, a lockshield valve should generally be left alone.
How to Choose the Right Radiator Valves
Consider the Room's Purpose
Start by thinking about how consistently the room is used. Rooms with irregular occupancy — a home office, spare bedroom, or dining room — benefit most from TRVs or smart valves, since there's little point in heating them fully when they're empty. Rooms you want at a constant temperature, like a hallway or bathroom, can work perfectly well with simple manual valves or a TRV set to a fixed position.
Think About Your Heating System
Not all valves are compatible with all systems. If you have an older gravity-fed system with a header tank in the loft, you'll need low-pressure compatible valves. If you have a modern sealed pressurised system or combi boiler setup, standard valves will work fine. Always check the pressure and flow rate ratings on any valve before purchasing.
Match the Connection Size
Radiator valves come in different pipe connection sizes, with 15mm being the standard for most UK homes. However, older properties may have 10mm or 12mm pipework, and some systems use 22mm connections for larger radiators. Measure your existing pipework or check with a plumber before ordering to avoid compatibility issues.
Choose the Right Flow Direction
Valves are manufactured in straight, angled, and corner configurations to accommodate different pipe entry points. If your pipes come up from the floor directly beneath the radiator, you need a straight or angle valve. If the pipes run along the wall and connect from the side, an angled valve typically provides the neatest finish. Corner valves handle pipes that enter from the floor at the end of the radiator.
Consider the Aesthetic
Since valves are visible components of your radiator, appearance matters — especially in living rooms and bedrooms. Standard valves come in white plastic, but you can also find them in chrome, brushed nickel, matte black, brass, and anthracite. Designer radiator valves with smooth minimal heads can significantly elevate the look of a premium radiator, while more traditional styled valves suit period homes and classic column radiators.
Energy Efficiency Goals
If reducing your heating bills and carbon footprint are priorities, TRVs should be considered the minimum on all radiators except the one in the room with your main thermostat. Smart valves take this further still by eliminating the guesswork entirely and giving you data-driven control over every circuit in your home. Studies have found that fitting TRVs across a home can reduce heating energy use by up to 20%, with smart systems pushing that figure higher.
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