TRVs Explained: How Thermostatic Radiator Valves Work

What Is a TRV?

A Thermostatic Radiator Valve (TRV) is a self-regulating valve fitted to individual radiators. Unlike a standard lockshield valve (which is set and left), a TRV automatically adjusts the flow of hot water to the radiator based on the temperature of the surrounding air.

TRVs were made compulsory in new builds and replacement heating systems under Part L of the Building Regulations, so most modern UK homes will have them.

How Do TRVs Work?

Inside the valve head is a wax or liquid element that expands and contracts with temperature. When the room warms up:

1. The element expands

2. This pushes a pin down into the valve body

3. The valve partially or fully closes

4. Less hot water flows into the radiator

5. As the room cools, the process reverses

The numbered dial on the TRV head sets the target temperature — not the radiator temperature directly.

TRV Number Settings

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Most living rooms and bedrooms are comfortable at setting 3 (around 20°C). Bathrooms and hallways can often be kept lower.

Common TRV Mistakes to Avoid

Stuck TRVs

If a radiator stays cold even with the TRV open, the pin inside the valve may be stuck. This is a common problem on older valves after summer. You can sometimes free it by removing the TRV head and pushing the pin manually — but if in doubt, have it replaced.

For TRV replacements, smart valve upgrades, or heating controls advice, contact Halo Heating on 01483 676108.