Guide · Home heating

Heating controls and boiler flow temperature

Good controls heat the rooms you use, when you use them. A condensing boiler also works more efficiently when the water in its radiator circuit is not run hotter than it needs to be. Stored hot water follows different rules.

By energy.org.uk editorial team · Reviewed by energy.org.uk editorial team · Published and updated 2 October 2026

Who this is useful for

Homes with a gas, LPG or oil boiler and radiators.
Anyone with a programmer, room thermostat, radiator valves or a smart thermostat they are not sure how to set.

If you have a heat pump, read heat pump flow temperature instead.

What to check first

Your boiler type. A combi boiler heats water on demand and has no hot-water cylinder. A system or regular boiler heats a cylinder, usually in an airing cupboard.
The boiler’s settings. Many boilers have one setting for the radiators (central heating) and a separate one for hot water. The manual explains which is which. Note and photograph the current settings before changing anything.
Your controls. Energy Saving Trust says boiler systems should have at least a programmer, a room thermostat and thermostatic radiator valves (TRVs).
Who lives in the home. Babies, older people and anyone who is unwell may need a warmer home. Comfort and safety come first.

How the main controls work

Programmer or timer: sets when the heating and hot water come on and go off.
Room thermostat: keeps the home at the temperature you set. It switches the heating off when that temperature is reached.
TRVs: limit the temperature in individual rooms by reducing the flow through each radiator. They sense the air around the valve, so keep radiator covers, curtains and furniture clear of them.
Weather compensation: where fitted and compatible, adjusts the flow temperature automatically as the outdoor temperature changes.

Radiator flow temperature and stored hot water

These are two different settings. Change the right one.

Radiator (central heating) flow temperature

This is how hot the boiler makes the water sent to the radiators. Nesta found that condensing combi boilers are often set to 70°C to 80°C by default. At those temperatures the boiler does not condense, so it misses its best efficiency.

If your rooms still reach a comfortable temperature, a lower radiator setting can help the boiler condense more often. Nesta suggests trying around 60°C in winter and lower in milder weather. Change it in steps and see how the home feels over a few cold days.

Stored hot water (cylinder)

If you have a hot-water cylinder, it must get hot enough to control Legionella bacteria. HSE guidance is to store hot water at 60°C or higher.

On many systems the same boiler flow heats the cylinder. Energy Saving Trust advises not setting the flow below 65°C on these systems, so that the cylinder can still reach 60°C. If your system has separate controls, or you are unsure how it is set up, ask a heating engineer.

Combi boilers

Lower only the radiator setting to change heating efficiency. The hot-water setting on a combi controls the temperature of water at the taps. Very hot tap water can scald, so take care with anyone vulnerable.

When not to lower the flow temperature

The home does not get warm enough at lower settings.
Someone in the home needs higher temperatures for health reasons.
Radiators are too small for the rooms, or the system needs balancing or repair. A heating engineer can check.

At a lower flow temperature, rooms may take longer to warm up. You may need to start the heating a little earlier.

Practical next steps

Find the boiler manual and note the current settings.
Set the programmer around when you are home and awake.
Set the room thermostat to the lowest temperature that is comfortable, and use TRVs to keep unused rooms cooler.
Lower the radiator flow temperature in small steps, if your rooms stay warm enough. Leave cylinder settings alone unless you know how your system works.
Bleed radiators that are cold at the top, and ask an engineer to balance the system if some rooms heat much more slowly.
Have the boiler serviced regularly by a registered engineer. Ask about weather compensation if your boiler supports it.

Important limitations

Savings depend on the boiler, radiators, your home and how you use the heating. We do not give a single figure.
These tips do not apply in the same way to storage heaters, heat pumps or heat networks.
An engineer should check the system if it does not heat properly, makes unusual noises or shows a fault.

Related tools and guides

Sources

Official sources checked 2 October 2026.