For most homes with a modern condensing boiler, a radiator temperature of around 60°C is a good place to start in winter, rather than the 70°C to 80°C many boilers are left on. If you have a hot water cylinder, the water stored in it should still be heated to 60°C, whatever you do with the heating.
This post explains the two temperature settings on your boiler, why a lower setting can use less gas, how to turn it down safely and when to leave it to a Gas Safe engineer. Everything here is done from the boiler's front controls or display. You never need to remove the boiler's casing.
The two temperatures your boiler controls
Most boilers have two settings. The heating setting, often shown with a radiator symbol, sets the flow temperature. That's how hot the water is when it leaves the boiler and heads round to your radiators.
The hot water setting, often shown with a tap symbol, sets how hot the water is at your taps on a combi boiler. On a system or regular boiler with a hot water cylinder, it controls how hot the cylinder gets.
Neither of these is your room thermostat. The thermostat decides when the heating comes on and how warm you want the room. The flow temperature decides how hot the radiators get while the heating is running.
Why a lower flow temperature can use less gas
Almost every gas boiler fitted in UK homes in recent years is a condensing boiler. It recovers extra heat from its own exhaust gases, but only when the water coming back from the radiators, called the return, is cool enough. That usually means below about 55°C.
When the flow temperature is set high, the return stays hot, the boiler can't condense and more heat goes out of the flue, the pipe that carries fumes outside. Research by the innovation charity Nesta found that many households could cut their gas use by turning a combi boiler's flow temperature down to around 60°C, without their homes feeling colder.
The trade-off is that radiators feel cooler to the touch and rooms can take a little longer to warm up. The boiler works for longer at a gentler, more efficient setting.
What setting to start with
- Combi boiler heating: try about 60°C. Many dials don't show numbers, so check the manual to see which mark is closest.
- Combi boiler hot water: a combi heats water as you use it rather than storing it, so a setting that feels comfortable at the tap is fine. Very hot water only ends up mixed with cold.
- System or regular boiler with a cylinder: you can lower the heating in the same way, but the cylinder must still reach 60°C. Stored warm water below that can let legionella bacteria grow, the cause of Legionnaires' disease.
On some older boilers one dial controls both the heating and the cylinder. Turning it down could stop the cylinder getting hot enough. If you're not sure how yours is set up, leave the setting alone and ask an engineer.
How to turn it down safely
- Find your boiler's manual, or look it up on the manufacturer's website, and search for "central heating temperature" or "flow temperature".
- Turn the heating dial, or the setting on the display, to about 60°C. Use only the controls on the front of the boiler.
- Leave it for a few days, ideally including a cold spell, so you can see how the house copes.
- If every room is warm enough, you could try a little lower, such as 55°C. If not, turn it back up in small steps.
Because the radiators run cooler, the heating may need to be on a little longer to reach the same room temperature. Starting your heating timer 15 to 30 minutes earlier on cold mornings usually sorts this out.
When a lower setting doesn't suit your home
Some homes struggle at 60°C on the coldest days. Older houses with less insulation, rooms with small radiators and draughty extensions are the usual ones. In those homes it's fine to turn the setting up during a cold snap and back down when the weather eases.
If one or two rooms always lag behind, the radiators may need balancing, which means adjusting the valves so hot water reaches each one evenly. Our guide to radiator balancing for hot and cold rooms walks you through it. If radiators are cold at the bottom or patchy, sludge in the system is more likely to be the problem than the setting, and power flushing may help.
Some heating controls can adjust the flow temperature for you, turning it up on cold days and down on milder ones. If you're thinking about new controls, our smart thermostat installation page explains what we fit.
When to call a Gas Safe engineer
Changing the temperature on the front of the boiler is safe for anyone to do. Call a Gas Safe registered engineer if:
- the boiler shows a fault code or locks out after you change the setting
- the setting sits behind a menu that asks for an installer code
- you have a cylinder and aren't sure it's still reaching 60°C
- the boiler keeps switching on and off every few minutes
- the radiators stay cold even with the setting turned up
Never open the boiler's casing or try to adjust anything inside it. Only a Gas Safe registered engineer should work on the gas parts of a boiler.
Keeping your boiler efficient this winter
A lower flow temperature works best on a boiler that's in good order. During an annual service the engineer checks the burner, the gas rate and pressure, the flue and the safety controls, and it's a good moment to ask about your temperature settings too.
If you'd like your boiler checked before the coldest weather arrives, B.Brill Plumbing & Heating LTD services boilers across Milton Keynes and the surrounding towns. You can book through our boiler servicing page.
