Avoid this radiator mistake that can increase your bills

Careful use of heater controls help you keep your heating bills in check. But by having all your radiators turned down but your thermostat up high you could be wasting money on gas and not feeling the benefit.  

Your thermostat tells your boiler when to run and when to stop. If you have modulating controls, it will also tell your boiler how hard it should work.

Thermostatic radiator valves (TRVs) have a different purpose, though. They decide how warm a room should be before radiator valves close and hot water doesn't run through a radiator anymore. They allow for control of your heating room-by-room.

Together, your room thermostat and your radiator valves make sure you only use the energy you need in a directed way. 

But if you use them wrong, you'll be wasting energy.

That's because if your thermostat is telling your boiler it's too cold, while your radiators aren't letting the warm water in, your boiler will just keep sending hot water around your pipes in a circle, wasting energy in a cold house. So it's important to make sure your thermostat, boiler and valves are all working efficiently together.

Get more tips for getting your heating set up this winter in our guide to reducing your heating bills.

The radiator and thermostat set up to avoid

Having your thermostat set to a high temperature but the radiator nearest to it turned down or turned off can be wasteful. 

Your boiler will be running for longer than necessary but you won't get the heat benefit. Here's why. 

Radiator valves stop hot water from flowing into a radiator when a certain room temperature is met. Each setting corresponds broadly to a range of temperatures:

• Setting zero will keep your radiator valves closed completely.
• The frost protection (*) setting will open the radiator valves if your room risks freezing. 
• Setting one will leave your room cold.
• Setting two will close the valve when the room is cool. 
• Setting three will close the radiator when the room is comfortable. 
• Setting four will close the radiator when the room's toasty.
• Setting five will keep the valve fully open.

But thermostatic radiator valves don't decide whether the boiler is heating up water for your central heating system or not. The room thermostat decides this. 

Your boiler will create hot water for as long as your thermostat tells it it needs to be on, and this hot water will flow around your pipes, into your radiators and back to the boiler.

If your thermostat is set to 20°C but it's in a room in which radiators are turned down to low settings or turned off, your thermostat will continue asking your boiler to run while your radiators refuse the hot water circulating around your home.

To make sure you only ever heat as much gas as you need, put your thermostat into the room you plan on heating up the most – perhaps the living room – and make sure that it's only requesting central heating from your boiler when you need it.

Which? testing has found the best smart radiator valves based on ease of use, temperature sensing, digital security and features available. Read our smart radiator valves reviews to find a Best Buy set.

How to best set up your thermostat and central heating

The temperature you set for your room thermostat should be able to be easily reached by the radiators nearby, so that when it's at that temperature your boiler turns back off. 

This means making sure the thermostat is in the room you want to be warmest and that the radiators nearby are allowed to heat fully. Or turning down your wall thermostat if you're finding it's coming on when you don't want it to.

Ideally, the radiator closest to your thermostat should be turned up fully so that the room quickly gets up to temperature and then your thermostat signals to your boiler to switch back off.

The lowest thermostatic setting that's healthy for people to spend a lot of time in is 18°C.

Meanwhile, other rooms in your home that don't need to be heated up can be set to lower radiator valve settings. The boiler will turn off when your main room is up to temperature, but unoccupied or lesser-used rooms won't have been heated up as much as their radiators will have stayed cool.

Do thermostatic radiator valves save money?

TRVs enable room-by-room control and better management of your heating, so they will save you money if used correctly. 

Your boiler doesn't know what your TRVs are doing, so it will send a flow of hot water around your house regardless of the setting your radiators are on — even if they're all off.

When a radiator's valve is closed, hot water doesn't flow into it. Instead, it continues on its route around your home having lost less heat. When it meets a radiator that does have open valves, the water will be hotter and that room will heat up more quickly. 

Eventually, the water returns to the boiler having cooled down on its journey.

So having some radiators closed off saves you energy overall as the heat is better directed towards rooms where you do want to increase the temperature. You're not wasting heat on radiators in empty rooms becoming hotter than needed.

That said, you do want the water returning to the boiler to have lost heat on the way, so that the boiler can condense. This helps a gas or oil boiler boiler run more efficiently. 

Whether it's best to turn unused radiators off or run radiators at low settings can depend on your home and the way your boiler's set up. 

But turning radiators in unoccupied rooms to low settings will suffice most of the time. A little water will move around them and help your boiler to condense, and it will prevent damage from damp and freezing. But the majority of your energy will be used on heating the room where the thermostat is placed, so that the boiler turns back off nice and quickly and stops burning gas at all.

If you've not adjusted your combi boiler's flow temperature yet, that can also save you money. Read our one simple trick for combi boiler owners to lower their heating bills to find out how.

How boiler controls can be more efficient

Many people have systems installed that don't make full use of the boiler's capabilities, so if you're having your boiler serviced it's worth asking your engineer if there's anything you could do to have it run more efficiently.

The most rudimentary boiler controls are on/off. The thermostat turns the boiler on when it detects that the air temperature around it is lower than the temperature it's set to. It then turns the boiler off again when this temperature is detected.

But these are some functions that can improve a heating system's efficiency:

• Load compensation. Ideally, boilers shouldn't need to run at full tilt every time they're on. Some can modulate according to how much heat the home needs. Boilers and thermostats that are connected in a network such as OpenTherm use less energy when only a small burst of heating is required. 
• Weather compensation. Common in many other European countries, some thermostats account for the weather outside, using an exterior sensor to determine how much heat the boiler needs to provide. Less on mild days, and more during cold snaps. 
• Smart technology. Although not a cure-all (and smart systems can run in rudimentary ways), smart thermostats and radiator valves allow for automated scheduling, and features such as open-window detection, which turns your heating off if it senses a wasteful draught. 

New gas boiler installations should include at least one of the above (or a fourth option: a flue gas recovery system). If this isn't offered to you, you should ask your installer why, as this is required under 2018's Boiler Plus regulation. 

Before you buy a new boiler, check out our boiler reviews to find a brand that's proven to be reliable in people's homes.