I’m a plumber

Jun 05, 2023

HOUSEHOLDS are only just realising what the numbers on radiator knobs actually mean.

And with energy bills soaring across the UK, using a thermostatic radiator valve (TRV) correctly could potentially half your gas bill.

If you've got a TRV attached to your radiators, you'll be able to limit or turn off the flow of hot water into the radiator.

This can help reduce the amount of gas that your boiler needs to burn to heat up the water in your central heating system.

A study by Salford University found that a typical central heating system uses 42% less gas when radiators are fitted with these gadgets.

The Sun spoke to Nathan Martin-Nicholls, a plumber at INHOUSE Plumbing and Heating to find out exactly what those numbers on our TRVs really mean.

Nathan said the most common question that he gets asked as a plumber is: "What do the numbers on a thermostatic radiator valve mean?"

He said that most people assume that they refer to the temperature of the radiator.

In fact, this is totally incorrect and the numbers carry a completely different meaning.

"The numbers actually relate to the temperature in the room, not the temperature of the radiator," according to Nathan.

The whole point of a TRV is to detect the temperature of a room and then control how much hot water is let into the radiator.

So if the room is cold, the TRV will sense this and allow more hot water into the radiator to heat up the room quickly.

As the room gets warmer, the TRV will restrict the amount of hot water coming into the radiator to maintain the temperature of the room.

And as the room temperature starts to drop, the TRV senses the temperature and will allow more hot water in again, repeating the process.

Nathan said that the number settings on the TRV roughly correspond to the room temperatures below:

Nathan said: "TRVs are a simple way to give you full temperature control on radiators in any rooms where you have the TRVs installed.

"The main benefit to them is that they will save you money on your heating bills, if you use them correctly."

The average household can save up to £75 every year if they have thermostatic radiator valves fitted on all their radiators, according to British Gas.

Valves can be picked up for less than £4 and they're easy to replace yourself if some of yours are not working.

Households can also get their hands on smart TRVs which can be controlled via an app but these are more expensive with prices starting at £38 from Toolstation.

During the winter months, Nathan recommended households to set their TRV to 2 or 3 in smaller rooms.

He said: "If you go into a room that is cold and the radiator is burning hot, leave it alone and don't adjust it. Let it do its job and allow the TRV to heat the room accordingly.

Those going away this winter should keep their radiator TRV on the lowest setting so that the radiators will come on for a short while if the temperature drops below 7°C.

Nathan warned against turning your TRVs to five.

"If you turn a TRV up to five, basically you are telling it not to stop letting hot water into the radiator until the room reaches a very very high temperature (around 30°C).

"If the temperature drops below 30 degrees, hot water will be allowed into the radiator to heat the room."

Households should only have TRVs on five or their maximum setting in rooms where you need the short and sharp heat.