Radiator valves explained: lockshields, wheel heads and TRVs

Most radiators in UK homes have a valve at each bottom corner. One is the control you use. The other is set once and left alone. Knowing which is which explains a lot of radiator problems, and helps you decide what you can do yourself and what needs a plumber or heating engineer.

This guide is about the radiator valves only. Nothing here involves the boiler. Anything to do with the boiler's gas side or casing is for a Gas Safe registered engineer. Plumbed towel rails use the same kinds of valve; see heated towel rails.

The three kinds of radiator valve

Lockshield valve. Usually under a plain plastic cap that just pulls or unscrews off, with a small spindle underneath that needs a spanner or a lockshield key to turn. It is set when the system is balanced, so each radiator gets its fair share of hot water, and then left. Balancing is covered in our guide to bleeding and balancing radiators. Do not turn lockshields to control room temperature. If you have to close one, count the turns so you can put it back where it was.

Manual wheel-head valve. A simple on/off control with a round head that you turn by hand. It does not respond to the temperature of the room. Fully open, it lets the radiator run as hot as the system allows.

Thermostatic radiator valve (TRV). A valve body with a sensing head on top, usually numbered from a frost or star setting up to 5 or 6. The head contains a wax or liquid element that expands as the room warms and gradually closes the valve. As the room cools, it opens again.

What the numbers on a TRV mean

The numbers are not a radiator power setting. They are a target room temperature. A TRV on 3 does not make the radiator "a bit warm". It lets the radiator run at full heat until the air round the valve reaches roughly the temperature that setting stands for, then closes down. The exact temperatures vary by maker. Wickes lists the Primaflow TRV below as covering 6°C to 28°C, for example, but check the leaflet for your own valve.

Turning a TRV right up does not heat a room faster. It just lets the room get hotter before the valve closes.

A TRV only works if it can sense the room. A TRV behind a long curtain, under a shelf or boxed in by a radiator cover will feel the heat from the radiator, not the room, and close too early. The Primaflow listing at Wickes also says its TRV should be installed on a two-pipe heating system. If you have older single-pipe heating, ask a heating engineer before changing valves.

A radiator that will not warm up

Go through the simple things first.

1. Both valves open? Check the TRV or wheel head is turned up. If the lockshield cap is off, check the spindle has not been fully closed.
2. Cold at the top only? That is usually air. Bleed it. See bleeding and balancing radiators.
3. Cold at the bottom or in patches? Often sludge, which bleeding will not fix. That is a job for a heating engineer. See heating sludge and inhibitor.
4. TRV turned up, radiator still cold, others fine? The pin under the TRV head may be stuck down. This is very common after the summer, when the valve has sat closed.

Freeing a stuck TRV pin

1. Turn the heating off and let the radiator cool.
2. Turn the TRV head to its highest setting, then remove the head. Many unscrew with a collar or ring; some have a release button or clip. The radiator stays full and the valve body stays in place, so no water should come out when only the head is removed.
3. You will see a small metal pin sticking up from the valve body. Press it gently. It should move down and spring back up.
4. If it is stuck down, work it gently with your fingers or tap it lightly with something soft. Do not use grips on the pin or bend it.
5. Refit the head and turn the heating back on.

If the pin will not move, or water appears round it, stop. The valve may need replacing.

A radiator that will not turn off

• With a wheel head: the valve's internal seal may be worn. A plumber can usually fix or replace it.
• With a TRV: remember a TRV on its lowest setting is a frost setting, not off. It will open again if the room gets cold. Some TRVs have a true off position; many do not. A pin stuck in the up position will also stop it closing.

To take a radiator out of use, for example to decorate, turn the TRV or wheel head off and close the lockshield, counting the turns. If water still gets through, one of the valves is not sealing and a plumber should look at it.

Replacing a TRV: what is involved

Changing a TRV head only, to a new head that fits the same valve body, is usually straightforward, because the head is not in contact with the water. Check the new head is compatible with the valve body. Heads from one maker often do not fit another maker's body without an adaptor.

Changing the whole valve body is a bigger job, and it is commonly done by householders who are confident with compression fittings. In outline:

• The radiator must be isolated or drained. The valve you are replacing cannot isolate itself. That usually means draining the system down below that radiator, or draining it fully. On a sealed system, the system then has to be refilled and repressurised following the boiler maker's user instructions. On an open vented system, the loft feed refills it. If you are changing the whole radiator, see radiator replacement.
• The new valve needs to match the pipe size (usually 15mm), the thread on the radiator tail, and the direction of fit (angled, straight or corner).
• Heating systems often contain inhibitor and dirty water. Protect floors, and dispose of it properly.

Stop and call a plumber or heating engineer if:

• the old valve or radiator tail is seized, or the tail starts to twist with the valve;
• the radiator tail leaks after refitting, or the joint will not seal;
• the radiator will not isolate and you are not sure how to drain your system;
• you have a sealed system and do not know how to refill it, or the pressure keeps dropping afterwards;
• the pipework is plastic and you do not know how it has been jointed;
• anything involves the boiler. Do not touch the boiler's gas side or open its casing.

Our guide to push-fit, compression and soldered joints explains the common joint types, and the plumbing tool kit covers the tools.

Radiator valves at Wickes

We haven't tested this. Figures are as the maker states them (checked 13 November 2026).

What number should my TRV be on?

There is no single right number. Start in the middle, around 3, and adjust a step at a time over a day or two. Rooms you use less, like bedrooms, often suit a lower setting.

Can I fit TRVs on every radiator?

Not always. The room with the main heating thermostat usually has a manual valve instead, so the TRV and the thermostat do not fight each other. Ask a heating engineer if you are not sure how your system is controlled.

Do I need to drain the system to change a TRV head?

Not normally. The head sits on top of the valve body and is not in contact with the water. Changing the valve body itself is different and means isolating or draining the radiator.