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Plumber explains what radiator numbers really mean and why you should 'leave it' at 3


With winter now in full swing, households are being urged to familiarise themselves with their radiators to help save on climbing energy bills.

Energy experts have hailed the importance of understanding how to use appliances and the thermostatic radiator valve (TRV), typically located on the side of the radiator.

This crucial component, marked with a series of numbers, regulates the flow of hot water into the radiator, thereby controlling room temperature.

Proper usage could potentially result in significant savings on energy bills, which continue to soar for many.

To help people understand what these numbers signify and how to utilise the TRV for cost reduction, Nathan Martin-Nicholls, a plumber at INHOUSE Plumbing and Heating, has offered his expertise. 

Contrary to popular belief, the numbers on the TRV do not indicate the radiator’s temperature.

“The numbers actually relate to the temperature in the room, not the temperature of the radiator,” Nathan clarified to The Sun.

The TRV operates by gauging the room’s temperature and adjusting the hot water flow from the boiler accordingly.

As the room warms up, less water is released into the radiator to maintain a steady temperature. On the other hand, when the room cools down, more hot water is allowed in to increase the heat, the Daily Record reports. 

Nathan highlighted that the number settings on the TRV generally correspond to the room temperatures below:

  • 0 = 0°C (off)
  • ✱ = 7°C (usually shown as a snowflake or full stop symbol)
  • 1 = 10°C
  • 2 = 15°C
  • 3 = 20°C
  • 4 = 25°C
  • 5 = 30°C

He advises households to set their TRV to two or three in smaller rooms when the weather turns colder.

He said: “During the winter, I recommend that you set your TRV to two or three and leave it at that.”

He added that the TRV will be able top function on its own to heat the room as needed, and that you should “refrain” from cranking it up to the highest setting. 

British Gas also says that households could save up to £75 on their annual bills if they install TRVs on all their radiators.

These can be purchased from Amazon for as little as £9.88 for two, or from Screwfix for £9.99. Smart TRVs, which can be controlled via an app, are also available but come with a higher price tag – a pack of four TADO smart TRVs from Screwfix will set you back £169.99.

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