Thermostatic Radiator Valves Explained: How to Use Them to Save Energy
A thermostatic radiator valve (TRV) controls the temperature of an individual room by adjusting the flow of hot water into that radiator. The numbers on the head, usually 1 to 5 or a snowflake to 5, correspond to approximate room temperatures, not how hot the radiator gets. Setting lower numbers in rooms you use less, like spare bedrooms, and moderate settings in living areas cuts wasted heat. TRVs work alongside your main room thermostat and boiler controls, not instead of them. Used properly, they help the whole central heating system run more efficiently. How a TRV works The TRV head contains a wax or liquid sensor that expands as the room warms. As it expands, it pushes a pin that gradually closes the valve, reducing the hot water entering the radiator. As the room cools, the sensor contracts, the pin rises and more hot water flows in. What the numbers mean Numbers vary slightly between brands, but as a rough guide: Setting Approximate room temperature Typical use Snowflake Frost protection only Unused rooms in winter 1 Around 10 to 12°C Rarely used rooms 2 Around 15 to 16°C Hallways, spare rooms 3 Around 19 to 20°C Living rooms, bedrooms 4 Around 22 to 23°C Rooms where people need extra warmth 5 Around 25°C or more Rarely needed Check your TRV manufacturer’s guidance for exact figures. Common mistakes Turning the TRV to 5 to heat a room faster. It won’t heat faster; it just means the room overshoots. Putting a TRV in the same room as the main thermostat. The two can fight each other. The room with the main thermostat usually has a radiator without a TRV, or one set fully open. Blocking the TRV head with curtains or furniture, which makes it read the temperature wrongly. Turning TRVs fully off in rooms in winter, which can encourage condensation and damp. Getting the best from TRVs Set living areas around 3 and adjust to comfort Set bedrooms slightly lower Set rarely used rooms to 1 or 2 Keep doors to cooler rooms closed Use your programmer or smart thermostat to control when heating runs Common TRV problems Stuck pin: a radiator stays cold because the pin under the head has seized. It can sometimes be freed, but if you’re unsure, ask an engineer. Leaking valve body: needs a professional repair. Worn or cracked head: can often be replaced without draining the system. If several radiators aren’t heating properly, the issue may be the system rather than the valves, such as sludge or balancing. Smart TRVs Smart TRVs let you control each room from a phone app with individual schedules. They work well in homes with rooms used at different times, and pair with smart thermostats. If you’re getting a new boiler, it’s a good time to upgrade controls too. TRVs in West Sussex homes Many homes around Worthing, Lancing and Shoreham have older radiator valves that were fitted before TRVs became standard, or TRVs that have seized from years of disuse. Replacing or servicing valves is often a simple way to improve comfort and control. Frequently asked questions Should all radiators have TRVs? Most should, except usually the radiator in the room with the main thermostat. Building Regulations generally require TRVs on new or replacement systems. Why is my radiator cold even though the TRV is on 5? The pin may be stuck, the lockshield valve may be closed, or there may be air or sludge in the radiator. Try bleeding it first, then get it checked. Can I fit TRVs myself? Replacing a TRV head is simple. Replacing the valve body means draining down part of the system and is best left to a plumber. Get your heating controls checked If your radiators or valves aren’t working as they should, give us a ring on 01903 530 851 or drop us a message and we’ll come and take a look.




