Many heating systems are equipped with cylindrical controls on the side of radiators, which are often numbered.

According to experts, these are called thermostatic radiator valves (TRVs), and while many people think the numbers relate to the temperature of the radiator, they don’t.

Ryan Harrison from said: “TRVs are common on modern radiators and they work by limiting the amount of hot water that runs into them.

“People assume the numbers equate to how warm you want your radiator, for example, if you’re feeling chilly you might turn your control to five.

“But they actually work by responding to the temperature of the room they are in.

“When the room reaches the required temperature as set on the valve, they restrict the amount of hot water going into your radiators and this stops them from getting any warmer.

“Zero means the radiator is shut off, while the rest roughly go up in five-degree increments.

“The exception is the snowflake symbol, which is roughly seven degrees.

“The rest are 1 = 10C, 2 = 15C, 3 = 20C, 4 = 25C and 5 = 30C.”

Ryan said to get the greatest benefits households need to treat the radiators in each room differently according to their use.

TRVs are all about giving everyone greater control when it comes to heating their homes so they are not heating rooms they don’t use.

The expert noted: “For example, rarely-used spare rooms don’t need to have their radiators set to five. You might be able to use them at one instead.

“Living rooms might be set at two or three, which will allow the space to warm up to a comfortable temperature without your boiler working in overdrive.

“It’s important to remember that little changes such as this can make big savings for the year, which is really important as we head into the colder months and the cost of living is putting even more pressure on people’s finances.”

If you suffer from mould within the home, turning the radiators up to a higher number may help, especially in the coldest months of the year.

It is also important to ventilate the home even with the heating on to prevent mould and condensation.