Could turning down your combi boiler save you £57 a year?

Written by Al Baker | Founder & Editor, The Penny Pincher - Last updated: the 3rd of November 2026

If your room thermostat says 20°C but the radiator setting on your combi boiler says 75°C, those numbers are doing two different jobs. You can leave the room thermostat where you like it and try sending slightly cooler water around the radiators. Nesta estimates that moving a suitable gas combi boiler from 75°C to 60°C could save around £57 a year, provided the house still gets warm enough. The first thing to find out is which sort of boiler you have.

What does the radiator setting on a combi boiler actually do?

On a gas combi boiler, the radiator symbol usually marks the central-heating flow temperature. That’s how hot the boiler makes the water before it travels through your radiators. The thermostat on the wall measures the air in the room, while the tap symbol on the boiler controls the hot water you wash with.

Think about the first hour of heating on a cold morning. At a lower flow temperature the radiators may feel cooler and the room may take longer to warm up, even though you’ve left the wall thermostat alone. The benefit is that cooler water returning to a condensing boiler lets it recover more heat from the exhaust gases. The test is whether the room is warm when you need to use it.

Which homes can try the 60°C setting?

Nesta’s free boiler walkthrough is for gas combis that heat tap water on demand and don’t have a separate hot-water cylinder. If you have a cylinder in an airing cupboard, for example, stop there. On a conventional system the boiler can also be responsible for heating stored water to a safe temperature. Energy Saving Trust explains why these systems need different settings. If you’re unsure which system you have, look up the model or ask your installer before changing anything.

If yours is a suitable combi, take a photo of the original radiator setting so you can put it back. Use the boiler manual or the walkthrough to find the heating control, then try lowering it gradually towards 60°C if it’s currently higher. Leave the tap setting alone. If your heating adjusts automatically to the outdoor temperature, ask your installer before altering the controls.

Try the change on a day when you can tell how the rooms feel. If the living room is still chilly by the time you sit down, or the bathroom isn’t warm enough in the morning, turn the flow temperature back up. Older people, people with limited mobility and those with some health conditions may need a warmer home. The Met Office’s winter warmth guidance is a useful starting point if anyone in your household is particularly affected by the cold.

Where does the £57 saving come from?

Nesta estimates that about 7.5 million UK households could make this change. Its evidence for the Money Saving Boiler Challenge draws on tests at the University of Salford’s Energy House. For a home starting at 75°C, Nesta used an estimated annual saving of 720 kilowatt-hours of gas. At the 7.97p per kWh used in its October 2026 figures, that works out at £57.38.

If you pay 6p per kWh for gas, saving the same 720 kWh would take £43.20 off your annual bill. How much gas you actually save depends on your home, the size of your radiators and how long you have the heating on. Your boiler’s starting temperature matters too. Nesta’s £57 estimate is based on lowering the radiator setting from 75°C to 60°C, so if yours is already at 60°C, that particular saving doesn’t apply.

How do six changes add up to an estimated £220?

Nesta also commissioned Cambridge Architectural Research to look at what happens when households make several changes together. Its six-measure package includes the boiler adjustment, so £220 is the modelled annual total with that £57 already included. The individual figures below show which changes might be relevant in your home. You can’t add them up to predict your bill, because they can save some of the same gas.

Take hot-water preheat as an example. On some combis it keeps a small amount of water hot between uses so there’s less of a wait at the tap. Switch preheat off and the boiler can still supply hot water on demand, but you may wait a little longer for it to come through. If preheat is already off, there’s nothing extra to save from that part of the calculation.

The same logic applies to room temperatures. If your thermostat already sits at 19°C, Nesta’s estimate for moving from 20°C to 19°C doesn’t apply to you. A thermostatic radiator valve lets you adjust an individual room, so a spare room that’s warmer than it needs to be might be a better place to start. The numbers on the valve are settings rather than readings in degrees, so make a small adjustment and see how the room feels. If you’re already keeping rooms colder than you’d like because of the cost, there’s also free help if you’re struggling with your bills.

The heating season Nesta modelled runs from October to the end of March. A cold April morning is still a cold April morning, so use the heating if your home needs it. If you want one thing to do today, look at the radiator setting and take that photo. It gives you a starting point for a change you can reverse, without committing the whole household to a colder winter.

Frequently asked questions

Will changing my combi boiler’s flow temperature make my shower colder?

On a combi with separate controls, changing the central-heating flow temperature leaves the tap and shower setting alone. Check the manual if the two symbols or menus aren’t clear.

What if my combi boiler is already set to 60°C?

You won’t get the modelled £57 saving by leaving it at 60°C. That figure assumes a starting temperature of 75°C, so there’s no reason to turn it up to match the example.

What should I do if the house feels too cold afterwards?

Raise the radiator flow temperature again if the rooms you use don’t reach a comfortable temperature when you need them. The original setting you photographed gives you a point to return to.

Can I use the same setting if I have a hot-water cylinder?

Don’t follow the combi walkthrough on a system with a separate cylinder. The boiler may also heat your stored hot water, so follow the instructions for that system or ask your heating engineer.