Which valve turns a radiator off?
The valve that turns a radiator off is the one you normally use to control it: the thermostatic radiator valve (TRV) with a numbered head, or a manual wheel valve on older radiators. The valve at the other end, usually under a plain plastic cap, is the lockshield. It is set once when the system is balanced and is only closed when you want to isolate the radiator fully.
| Valve | What it looks like | What it does | Use it to turn off? |
|---|---|---|---|
| TRV | Plastic head with numbers, often 0 or a frost symbol up to 5 or 6 | Opens and closes automatically to hold the room temperature | Yes, turn to 0 or the lowest mark |
| Manual valve | Plain round head or wheel, no numbers, sometimes marked + and - | Open or closed by hand | Yes, turn clockwise to close |
| Lockshield | Plain cap, often grey or white, that hides a small spindle | Sets how much water the radiator gets (balancing) | Only to isolate, together with the other valve |
Pipes can be connected at either end, so the TRV is not always on the same side. If both ends have plain caps, one of them is a manual valve with a cover, and the other is the lockshield.
How to turn off a radiator with a TRV
- Find the settings on the head. The Energy Saving Trust describes TRV dials as often numbered 0 to 6, where 0 is off and 6 is fully open. Many heads also have a frost symbol, a star or snowflake, at the low end.
- Turn the head to 0 if it has one. This closes the valve.
- If the lowest mark is the frost symbol, turn it there. The valve stays closed unless the room gets cold enough to risk frost, then opens a little to protect the pipes. For most rooms that is a sensible setting for a radiator you want off.
- Check after an hour of heating. The radiator should be cold or close to it, apart from a little warmth near the pipe connection.
A TRV head only presses a pin down to close the valve, and on older valves the seal is not always perfect, so a small amount of heat can still get through. If you need the radiator fully off, for example to take it off the wall, isolate it as described below.
At the end of the heating season, turn TRVs back up rather than leaving them at 0 all summer. A pin that sits pressed down for months can stick shut. Our guide to one radiator not heating explains how to free one.
How to turn a radiator off with a manual valve
Turn the manual valve head clockwise until it stops. That closes the valve and stops water flowing through the radiator. Do not force it past the point where it stops, as the spindle or its seal can be damaged. Turning it anticlockwise opens it again. If the head just spins without closing, the head has come loose from the spindle and needs refitting or replacing.
Turning off vs isolating a radiator
Turning off a radiator closes one valve, which stops heat but leaves the radiator connected to the system through the lockshield. Isolating a radiator closes both valves, so the radiator is cut off from the rest of the heating and holds its water on its own. You need to isolate a radiator before:
- taking it off the wall to decorate behind it or fit a new one
- replacing a bleed valve, TRV body or valve tail
- stopping a leak from the radiator itself while you wait for a plumber
For turning off a spare room for the winter, closing the TRV or manual valve is enough. There is no need to touch the lockshield.
How to isolate a radiator
- Turn the heating off and let the radiator cool.
- Close the TRV or manual valve fully. On a TRV, turning the head to 0 is not always a watertight shut-off. For a firm seal, unscrew the head and fit the plain manual cap that came with the valve, then turn it clockwise until it stops. If you have no cap, a plumber can supply one to suit the valve.
- Remove the lockshield cap. It pulls off or unscrews.
- Close the lockshield clockwise with a lockshield key or small adjustable spanner, counting the turns as you go, and write the number down.
- Check it is isolated. With the heating back on for the rest of the house, the radiator should stay completely cold.
When you have finished, reopen the lockshield by the same number of turns so the balance of the system is unchanged, then open the TRV or manual valve. If you took the radiator off, it will need bleeding once refitted. Our guides on how to remove a radiator and how to bleed a radiator cover those steps.
Isolating a radiator does not drain it. It still holds several litres of heating water under some pressure, and opening a nut or bleed valve lets it out. Old valves can also let water past slowly. Keep towels and a tray to hand, and if a valve weeps from the spindle as you turn it, stop and call a plumber.
Is it cheaper to turn off radiators in unused rooms?
Turning down radiators in rooms you do not use does save energy, because the boiler heats less of the house. The Energy Saving Trust advises setting each TRV to the lowest number that keeps the room comfortable, suggesting around 3 to 4 for the rooms you use most and 2 to 3 for bedrooms and rooms you use less. Which? makes a similar point: turning radiators in empty rooms down low is usually enough, and letting a little water move round them helps prevent damage from damp and freezing.
Turning a radiator fully off is a different matter. A room left completely unheated for weeks can cause problems:
- Damp and mould. Cold walls, especially outside walls, collect condensation from moist air drifting in from the rest of the house. Wallpaper, stored clothes and furniture against those walls are the first to suffer.
- Frozen pipes. In a hard frost, pipes in an unheated room on an outside wall can freeze. The frost setting on a TRV is there to prevent this.
- Heat loss from next door. Warm rooms lose heat through internal walls and under doors into the cold room, so part of the saving is lost.
The practical answer is to use the frost setting or a low number rather than off, keep the door closed, and open a window briefly now and then to let moist air out.
Radiators you should not turn off
Two radiators are best left on.
The radiator in the room with the thermostat
The wall thermostat decides when the boiler runs for the whole house. If the radiator in that room is off or turned right down, the thermostat never reaches its setting, so the boiler keeps running and the other rooms overheat. This is why guidance for new heating installations calls for TRVs on radiators in every room except the one with the room thermostat. That radiator usually has a manual valve instead, and it should stay open.
The bypass radiator on older systems
A boiler needs a minimum flow of water through it while it is firing. Many modern boilers have an internal or automatic bypass for this, but some older systems rely on one radiator, usually in the hall or bathroom, being left without a TRV so there is always an open route. Your boiler's installation manual states its bypass requirement. If you are not sure how your system is set up, do not close that radiator, and never turn off every radiator in the house with the heating running. If the boiler starts cutting out or making noises after you close radiators, reopen them and see our guide to a boiler that keeps turning off.
What to do next
If a TRV or manual valve will not turn, spins without closing, or the radiator stays hot when the valve is closed, the valve is probably worn. Our guide on how to change a radiator valve explains what is involved and when to leave it to a plumber. If a valve drips from the spindle or the nut underneath, put a container under it and call a plumber rather than tightening it hard. When you turn the radiator back on after a long spell off, check it heats evenly. A cold top means it needs bleeding.