Home / Guides / Thermostatic radiator valves
What are thermostatic radiator valves (TRVs)?
The numbered dials on the side of most radiators. Each one senses the room's temperature and turns that radiator down when the room is warm enough, so you heat rooms to suit how you use them.
- 1 to 5the numbers on most TRV heads
- 3a sensible starting setting for most rooms
Radiator valve
A TRV doesn't make the boiler work harder or the radiator hotter. It decides when that radiator has done enough.
Set sensibly, they stop you heating rooms that are already warm, which saves gas.
How a TRV works
A sensor in the head, a pin in the valve.
The head contains a sensor that expands as the room warms. As it does, it presses a pin in the valve and closes it, so less hot water flows into the radiator. When the room cools, the valve opens again.
The numbers aren't temperatures. On most heads, 3 is somewhere around 20°C, and each number up or down is a few degrees.
- Bedrooms kept cooler for sleeping
- Living rooms kept comfortable
- Spare rooms kept low when nobody's using them
Room by room
Where to fit them, and where not
Almost every radiator, with one exception.
TRVs work on almost every radiator in the house: bedrooms, living rooms, kitchens, hallways and home offices.
The exception is the room with your main wall thermostat, often the hall or landing. Leave that radiator without a TRV, or set it fully open. If both try to control the same room, the heating can switch on and off for no clear reason.
When a boiler is replaced, Scotland's guidance for heating installers expects room by room control like this, alongside a room thermostat.
Fitting a valve
Fitting new valves
Swapping the whole valve usually means draining some water from the system, so it's a job for us. Changing just the head on a compatible valve is simpler.
Manual or smart TRVs
| Manual TRV | Smart TRV | |
|---|---|---|
| How you set it | Turn the dial on the radiator | From an app, or the dial |
| Schedules | No | Yes, room by room |
| What it needs | Nothing | Batteries and the maker's thermostat or hub |
| Best for | Set it once and leave it | Rooms used at different times of day |
Hive and tado both make smart radiator valves. Our Hive or tado guide compares the two.
Which one sounds like you?
- One radiator won't come onStuck pin
Often freed or replaced on a visit.
- Valve drippingBook a plumber
A new valve or a reseal.
- Want room by room from your phoneSmart thermostats
Hive or tado, fitted and set up.
- Radiator cold at the topBleed it first
Air, not the valve.
Common questions
What number should I set my TRV to?
Start at 3 in most rooms, which is roughly 20°C, then adjust a step at a time. Bedrooms are often comfortable a step lower.
Why is my radiator cold with the TRV on 5?
The pin inside the valve may be stuck. With the head off, it should move in and out freely. If it's stuck, an engineer can free it or replace the valve.
Should every radiator have a TRV?
Almost every one, except the radiator in the room with your main thermostat.
Do TRVs save money?
They stop rooms being heated more than they need to be, which saves gas. How much depends on how you use the rooms.
Can I fit a TRV myself?
Changing the whole valve usually means draining water from the system, so we'd recommend an engineer. Changing just the head on a compatible valve is simpler.
Do smart TRVs work with my boiler?
They work with the maker's own thermostat or hub, such as Hive or tado. We can tell you what suits your system.
Related pages
Not sure what you need? Give us a shout.
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