Avoid this radiator mistake that can increase your bills

Careful use of heater controls helps you keep your 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.  

As we head into Autumn and nights (and days) get colder, many of us may be tempted to turn up the thermostat to fend off the chill. But misunderstandings about how your radiator valves and room thermostat work together could see you wasting energy (and money). 

Here's how to stay warm without bumping up your bills unnecessarily. 

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

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How do thermostats and radiator valves work?

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.

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, make sure that your thermostat is 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 set up your thermostat and central heating

A room thermostat stops your central heating system from using more energy than it needs to, by indicating to your boiler to turn off once it's reached a set temperature. 

You should set your thermostat to the lowest comfortable temperature for your needs. For most people, this is between 18°C and 21°C.

Make sure radiator valves near the thermostat are fully open. Meanwhile, other rooms in your home that don't need to be as hot can be set to lower radiator valve settings. 

The boiler will turn off when your main thermostat 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.

If you have a smart thermostat that you can move around, try it in different parts of the house to see where is best. It needs a free flow of air to get an accurate reading, so make sure it's not blocked by furniture or curtains, or too close to a source of heat. 

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 instantly. Read our one simple way to adjust your boiler to find out how to do it yourself.

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.