Should I turn my boiler’s flow temperature down?

Should I turn my boiler’s flow temperature down?

Everyone is looking for easy ways to cut their energy bills this winter, and one option being talked about is turning down your boiler’s flow temperature.  

But what does turning down the flow temperature mean, and is it a good idea? 

The first thing you need to know about is your boiler thermostat

What is a boiler thermostat and what does it do? 

The boiler thermostat is a control on your boiler that adjusts the flow temperature, which is the temperature of the water it sends to the radiators.  

The water cools as it flows through the radiators before it returns to the boiler. The temperature of the water at this point is the return temperature.   

Reducing the flow temperature also lowers the return temperature. All boilers are more efficient when the return temperature is low, and this can save you energy and money

Are boiler controls different from the heating controls? 

Your boiler controls are separate from your central heating controls, such as your room thermostat, programmer and radiator valves. The central heating controls turn your heating on and off, while the boiler thermostat changes the temperature of the water in the system. 

It’s important to get your heating controls right first before you try to adjust the boiler’s flow temperature with your boiler’s thermostat.  

How do I adjust the boiler’s flow temperature? 

Your boiler will have either a dial to control the flow temperature or some buttons and a digital display. You’ll probably need to open a flap on the boiler to access this – don’t worry, you’re allowed to open the flap.   

If you have a conventional boiler with a hot water cylinder, then there will be just one dial or setting to adjust.  

If you have a combi boiler with no hot water cylinder, then there will be two dials or settings: one for the radiators and one for the hot water. You need to adjust the one with a picture of a radiator next to it, not the one with a picture of a tap, which is for your hot water. 

Before you make any adjustments, it’s a good idea to take a photo or make a note of how everything’s set. That way you’ll know what to turn it back to if you need to.

What should I know before I turn down or adjust my boiler’s flow temperature?   

You don’t have to turn down your boiler’s flow temperature if you don’t want to. But if you decide to do it, these are your options depending on the type of boiler you have.  


Option one: turn it down to a level that’s just warm enough and leave it there 

This option assumes that the installer probably set the boiler thermostat to maximum when they fitted the boiler, and no one has adjusted it since. If that’s the case, then the flow temperature will be too high for most homes and heating systems, so you can probably turn it down. 

Combi boiler with no hot water cylinder 

If you have a combi boiler with no hot water cylinder, you can turn the radiator’s flow temperature down as much as you like without affecting the hot water. Some people suggest that turning the radiator flow down to 60 degrees is reasonable, but you’ll have to find what works for you by trial and error. Bear in mind there’s a risk of the house getting too cold while you find the right temperature.  


Option two: adjust the temperature occasionally when the weather changes 

This means going a step further and working out different temperature settings depending on the weather.  

If the weather is mild and you have a combi boiler, you’re more likely to be able to heat your home with a lower flow temperature, maybe 50 or 55 degrees. If it’s very cold, you’ll want to set it a bit higher. If you have a conventional boiler, you can’t go below 65 degrees, so it’s unlikely you’ll be able to do this.  

This approach will save you more money than option one, but there’s more of a risk that you’ll have a cold house at times.  


Option three: adjust the temperature constantly as the weather changes 

This isn’t something you can do on your own. You might be able to get a heating engineer to fit a weather compensator or a load compensator, which will change the flow temperature for you. You can only do this if you have a combi boiler. The engineer will still need to check if your boiler is compatible, and you’ll have to pay to have it fitted.  

Doing this will give you the maximum possible savings from adjusting the temperature of your boiler and should minimise the risk of your house not getting warm enough.