Thermostatic radiator valves: how to set them

Use the dial to find a comfortable room temperature, then let it do its job.

The answer in 2 lines. A thermostatic radiator valve, or TRV, senses the air around it and adjusts the hot-water flow through its radiator. Lower settings generally mean a cooler room; higher settings mean a warmer one. There is no reliable temperature conversion that fits every model. Keep the head exposed to room air, start with a middle setting and adjust gradually. A conventional TRV cannot make a cold radiator heat when the central heating is off.

The first 3 steps

Identify the control: a numbered or marked thermostatic head, rather than a plain manual valve or the covered balancing valve at the other end.
Start around the middle of the TRV dial in a room you use, then adjust towards the lowest setting that remains comfortable.
Move curtains and furniture away from the head so that air can circulate around its sensor.

Stop: danger

A leaking valve: stop adjusting it. Protect the floor if safe, tell your landlord if you rent, and arrange a qualified heating professional.
A stuck control: do not force it with pliers or undo pipe connections. Changing a normal setting should not involve dismantling the water-bearing parts.

What the dial actually controls

A TRV regulates room warmth by restricting or allowing hot water through the radiator. The radiator may cool once the room is warm enough, then warm again as the room cools. That can be normal operation rather than a fault.

The Energy Saving Trust’s heating-controls guide, updated in 2026 explains the mechanism and confirms that dial numbers do not represent identical temperatures across models. Read its TRV section instead of relying on a generic conversion chart.

Choose settings by use, not by room name alone

A spare room can usually be cooler than an occupied sitting room. A bedroom used all day may need a different setting from one used only for sleeping. Make a small adjustment, let the room settle and judge the room’s comfort rather than how hot the radiator feels.

Keep background warmth in little-used rooms during cold weather. The Centre for Sustainable Energy’s controls guide, reviewed in September 2026 explains why leaving rooms unheated for prolonged periods can encourage damp and mould. Use its radiator-valve section to plan which rooms need more or less heat.

What not to do

Treating the highest setting as a boost button: choose the temperature you actually want.
Hiding the sensor behind a curtain or inside a radiator cover.
Assuming a frost symbol is a comfortable occupied-room setting or protects the entire property.
Changing every valve and the room thermostat together, making the result difficult to assess.

Keep the sensor clear and understand the main thermostat

A head surrounded by trapped warm air may reduce the flow before the rest of the room is comfortable. This council home-user guide illustrates why TRV heads should not be shielded by curtains or furniture. Use it to recognise the arrangement, while following your own installation’s instructions.

The main room thermostat controls overall heating demand. Do not use a radiator valve to keep that thermostat’s room cold while the thermostat continually asks for heat. Arrangements vary, especially with connected controls: ask the installer or landlord how the controls should work together.

If turning the valve seems to do nothing

First establish whether the heating is running and whether other radiators are warm. Compare the room temperature with the setting: a radiator need not stay hot after the room is comfortable.

If the room stays cold, or overheats despite a low setting, record what happens and ask a qualified heating professional to investigate. Report which radiator is affected, whether others work, and whether there is noise or a leak. These observations help without committing you to a diagnosis or replacement.

Good to know

For health, government advice recommends at least 18°C in frequently occupied rooms. Read the keeping-warm section at GOV.UK when deciding whether a cooler room is suitable.
A connected radiator valve may have scheduling or heating-demand functions. Check the installed system’s instructions before assuming it behaves like a conventional TRV.
These operating principles apply across the UK. This guide is written for England; local housing and support arrangements differ elsewhere.

Illustrative example: in Nottingham, Ben’s sitting room feels chilly although the radiator starts hot. A long curtain encloses the valve head. He moves the curtain clear, leaves the dial at a moderate setting and observes the room before adjusting again. He avoids replacing the valve on guesswork.

A made-up story, for illustration.

Bobby

Sources, verification, confidence

Verified on 6 November 2026, for England. Confidence: high for how conventional TRVs work, keeping sensors clear and adjusting room by room; medium for troubleshooting without inspecting the system. No universal dial-to-temperature conversion is claimed. Connected controls and frost settings require the specific instructions.