How Does a TRV Work? Thermostatic Radiator Valves Explained
A thermostatic radiator valve (TRV) is one of the simplest ways to control your heating room by room and cut energy bills. Here's how a TRV actually works and how to get the best from it.
What is a TRV?
A thermostatic radiator valve is a self-regulating valve fitted to the flow side of a radiator. Instead of you turning the radiator on and off manually, a TRV senses the air temperature around it and automatically opens or closes to keep the room at the level you've set.
How a TRV works
Inside the TRV head is a sensor filled with a liquid or wax that expands as the room warms up and contracts as it cools. As it expands, it pushes a pin down to gradually close the valve and reduce hot water flowing into the radiator. When the room cools, the sensor contracts, the pin lifts and hot water flows again. Genuine Myson TRV2 valves use a fast-acting liquid sensor for accurate, A-rated control.
What do the numbers mean?
The numbers on a TRV head (usually 0–5, plus a frost/snowflake setting) are not temperatures — they represent a target room temperature range. As a rough guide: 0 = off, frost setting ≈ 7°C, 1 ≈ 15°C, 2 ≈ 18°C, 3 ≈ 20°C, 4 ≈ 22°C and 5 ≈ 24°C. Setting 3 suits most living spaces.
Do TRVs save money?
Yes. TRVs let you heat only the rooms you're using, and only to the temperature you need — so you're not paying to overheat spare rooms. Combined with a room thermostat and programmer, TRVs are one of the most cost-effective heating upgrades you can make.
Fitting tips
Don't fit a TRV in the same room as your main room thermostat — the two can fight each other. Keep the head unobstructed by curtains or furniture so it can sense the true room temperature. Modern Myson TRV2 valves are bi-directional, so they work whichever way the water flows.
Choosing the right TRV
Check your pipe size (usually 10mm or 15mm) and whether you need an angled or straight body. For a complete job, a radiator pack pairs the TRV with a matched lockshield valve.
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