Boiler flow temperature: the setting that cuts your gas use
Published 26 October 2026. Costs at the price cap for 1 October 2026 to 31 December 2026.
Your boiler heats water and pumps it round your radiators. The temperature it heats that water to is the flow temperature, and on many boilers it’s left at a high factory setting. Turning it down makes a condensing boiler more efficient, and for a typical household that’s worth about £68 a year.
Why lower is cheaper
A condensing boiler gets extra heat back from its exhaust gases, but only when the water coming back from the radiators is cool, around 54°C or below, Nesta explains. Most are set to 70 to 80°C, too hot for the water to come back that cool, so the boiler rarely condenses. High flow temperatures also make a boiler switch on and off more often.
The radiators run cooler, so rooms take a little longer to warm up, but they get there.
What it saves
Tests at the University of Salford’s Energy House, in Nesta’s evidence summary, measured the gas saved by lowering a combi’s flow temperature from 80°C:
| Flow temperature | Heating gas saved | All gas saved | A typical household, a year |
|---|---|---|---|
| 70°C | 5% | 3.9% | £30 |
| 60°C | 12% | 9% | £68 |
| 55°C | 16% | 12.1% | £92 |
The yearly figures are for Ofgem’s typical household, 9,500 kWh of gas a year, at the Great Britain average gas rate of 7.97p a kWh. “All gas” assumes heating is three-quarters of it, as Nesta did. If your boiler is already below 80°C, you’ll save less.
It isn’t free of trade-offs. In the same tests the house took 17 minutes longer to reach a comfortable temperature at 60°C, and averaged 0.5°C cooler over a day. Starting the heating 15 to 30 minutes earlier fixes that but gives back some of the saving, roughly 3 to 4 percentage points.
How to change it
- Find the heating control on your boiler. It’s usually a dial or button marked with a radiator symbol. The one marked with a tap is for hot tap water: leave that alone.
- Set it to 60°C. Some dials show numbers or dots rather than degrees, so check your manual for what each step means.
- Leave it for a few days, including a cold one.
- If rooms don’t get warm enough, turn it up by 5°C. If they do, try 55°C.
When not to
- You have a hot water cylinder. Stored hot water needs to stay hot to stop legionella. Ask a heating engineer, or don’t go below 65°C.
- You only ever heat one room. Nesta’s early modelling suggested gas use could rise slightly.
- Someone in the home is vulnerable to the cold. Start a little higher, and make sure they can turn it back up.
The other free setting
Many combis also keep themselves hot around the clock so the taps run hot sooner. Turning that off is a separate button, usually labelled eco: see preheat and eco mode. Thinking about a new boiler? The boiler size calculator works out what your home needs from your gas use.
Common questions
What should I set my boiler flow temperature to?
For a combi boiler, 60°C is the setting Nesta’s Money Saving Boiler Challenge recommends as a balance of savings and comfort. Many homes stay warm at 55°C or lower, which saves more. If rooms don’t get warm enough in a cold spell, turn it up by 5°C.
How much does lowering the flow temperature save?
In Nesta’s evidence, going from 80°C to 60°C saved about 9% of a combi household’s gas. For a typical household using 9,500 kWh a year, that’s about £68 a year at the current price cap.
Is flow temperature the same as the hot water temperature?
No. Flow temperature is the water the boiler sends round your radiators. On a combi, the hot tap water has its own setting, usually a dial marked with a tap symbol. This guide is about the radiator one.
Can I lower it if I have a hot water cylinder?
Take care. With a cylinder, the boiler also heats stored hot water, which must stay hot enough to stop legionella bacteria growing. Nesta advises leaving it to a heating engineer, or going no lower than 65°C.
Savings from Nesta’s Money Saving Boiler Challenge evidence summary. Gas rate from Ofgem’s price cap, checked 23 October 2026. Typical use from Ofgem’s typical domestic consumption values.