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Should I turn down my boiler flow temperature?
On most combi boilers, yes. Turning the heating flow temperature down to around 60°C lets the boiler run as it was designed to, and research for Nesta estimated it can cut a household’s gas use by about 9%.
- 60°Ca good starting point on a combi
- 9%estimated saving on the total gas bill
- 65°Ca safe setting with a hot water cylinder, says Nesta
60°Cstart here
Your boiler’s flow temperature is how hot it heats the water it sends round your radiators. It’s not the same as your thermostat, which sets how warm the room gets.
Most boilers in the UK are set to send water out at 70 to 80°C. That’s hotter than a modern condensing boiler needs, and it stops it working at its most efficient.
Turning it down is free, takes a minute, and you can always turn it back up. Here’s how, and when it’s best left alone.
Why it saves gas
It’s all about the water coming back.
A condensing boiler only condenses, and gets its extra efficiency, when the water coming back from the radiators is cool enough, around 54°C or below. At 70 to 80°C flow, it rarely is.
Turn the flow down to 60°C and the return water drops low enough for the boiler to condense. In tests for Nesta at the Salford Energy House, going from 80°C to 60°C cut the gas used for heating by 12%, which works out at about 9% of a typical total gas bill.
What will I notice?
- Radiators feel warm rather than too hot to touch
- Rooms take a little longer to warm up
- The heating may run a bit longer, but uses less gas
Combi boiler
How to do it on a combi
Check your manual if the controls look different.
Find the heating dial
Look for the control with a radiator symbol. Leave the one with a tap symbol alone, that’s your hot water.
Set it to 60°C
Some boilers show a temperature, some a number scale and some a menu. Your manual will tell you which setting is about 60°C.
Live with it for a week
If you’re comfortable, try 55°C. If the house struggles to warm up, go back up a little.
Turn it up in a cold snap
In very cold weather you can turn it up for a few days, then back down after. It also helps stop the condensate pipe freezing.
When to be careful
It doesn’t suit every home.
You have a hot water cylinder
The water stored in a cylinder needs to reach 60°C to keep legionella bacteria under control. Nesta says cylinder homes can safely go down to 65°C, and it’s worth asking an engineer to set it up.
Someone at home is vulnerable
If you’re looking after someone older, unwell or very young, start a little higher and come down slowly.
You only heat one room
Nesta doesn’t recommend lowering it if you’re only heating a single room.
Some rooms won’t warm up
A radiator that’s too small for its room, or a system that needs balancing or cleaning, will show up at lower temperatures. Turn it back up and ask us at your next service.
Set up at your service
We’ll set it for you
At your annual service we’ll check the flow temperature, hot water temperature and eco settings, and set them up to suit your home.
Which one sounds like you?
- Combi boiler, no cylinderSet it to 60°C yourself
Use the steps above.
- Hot water cylinderAsk at your service
We’ll set it safely.
- Can’t find the settingBook a service
£120 including VAT.
- Heat pumpHeat pump servicing
Heat pumps are set up differently.
Common questions
What should my boiler flow temperature be?
For most combi boilers, 60°C is a good starting point, and many homes are comfortable at 55°C. With a hot water cylinder, Nesta says 65°C is safe, ideally set up by an engineer.
Will a lower flow temperature damage my boiler?
No. Condensing boilers are designed to run at these temperatures. It’s how they get their best efficiency.
Is the flow temperature the same as my thermostat?
No. The thermostat sets how warm you want the room. The flow temperature sets how hot the boiler makes the water it sends to the radiators.
Will my house still get warm enough?
In most homes, yes, it just takes a little longer. If a room never gets warm, the radiator may be too small for it or the system may need balancing or cleaning.
Should I turn my hot water temperature down too?
On a combi, the tap temperature can often come down a little too. With a cylinder, the stored water needs to stay at 60°C, so leave that to an engineer.
Does eco mode do the same thing?
No. On many combis, including Worcester Bosch, eco mode turns off the preheat that keeps water warm for the taps. It’s a separate setting. Our guide to eco mode explains it.
Related pages
Sources: Nesta, Money Saving Boiler Challenge supporting evidence; Nesta, campaign summary. Checked 1 November 2026.
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