Glossary · Boilers and boiler types
What is the best boiler temperature setting?
The best boiler temperature setting is the lowest radiator flow temperature that still heats your home comfortably. For a modern combi, Vaillant puts this between 60 and 70°C, because a higher setting stops the boiler condensing. Hot water is set separately, and manufacturers give different figures, so check your own manual.
Key points
- Vaillant says a modern combi should run its radiator flow temperature at 60 to 70°C, and no higher, to stay in condensing mode.
- In spring and autumn Vaillant suggests 50 or 55°C for the radiators, at some cost to heating performance.
- The radiator dial and the hot water dial are two separate settings and they do not need the same number.
- Baxi and Vaillant give different hot water figures, so follow the manual for your own boiler rather than a single number.
- Room temperature is set on the thermostat, not on the boiler. Both manufacturers point to 18 to 21°C as a comfortable range.
How the boiler temperature setting works
Most modern gas boilers have two temperature controls. One sets the temperature of the water sent to your radiators. This is called the flow temperature. The other sets the temperature of your hot water. A combi boiler heats that water on demand, as described in how a combi boiler works.
Neither control is the temperature of your rooms. Vaillant is clear that the boiler temperature is the temperature of the boiler’s own water. The target for each room is set by your thermostat.[1]Vaillant, What temperature should my combi boiler be set at?
Why does the radiator number matter? A condensing boiler saves gas by pulling extra heat out of its exhaust gases, and it only does this when the water returning to it is cool enough. Vaillant says that above a flow temperature of 70°C a modern combi will not enter condensing mode and will not run at its best efficiency.[1]Vaillant, What temperature should my combi boiler be set at?
What the manufacturers recommend
The two manufacturers whose own pages we checked agree on the principle and differ on some figures.
| Setting | Vaillant | Baxi |
|---|---|---|
| Radiator flow, winter | 60 to 70°C | Says to set at least 65°C |
| Radiator flow, spring and autumn | Around 50 or 55°C | No separate figure given |
| Hot water | Around 50°C | Says not to go lower than 65°C |
| Room thermostat | 19 to 21°C | 18 to 21°C |
Vaillant also says that if you have improved your home’s insulation since the heating was installed, you may be able to leave the radiators at 50 to 55°C all winter. The lower the flow temperature, the more efficient the system.[1]Vaillant, What temperature should my combi boiler be set at?
Baxi makes the opposite point from the other end. It says setting the temperature higher gives hotter radiators but lowers efficiency, and that turning it to the maximum could cut efficiency by up to 20 per cent.[2]Baxi, What temperature should my boiler be set at?
The hot water figures are where the two disagree most. Vaillant says anything over 45°C at the tap or shower can scald, so hot water is mixed down with cold. Baxi says hot water should not be set below 65°C, so that bacteria such as Legionella do not grow.[1]Vaillant, What temperature should my combi boiler be set at?[2]Baxi, What temperature should my boiler be set at? Both statements are on the manufacturers’ own pages. They describe different boilers and systems, so use the figure in the manual for yours. If you have a hot water cylinder, ask your engineer which setting suits it.
One more point from Worcester Bosch. In prolonged freezing weather, it lists turning the boiler’s heating control to maximum as a way to reduce the risk of the condensate pipe freezing.[3]Worcester Bosch, Boiler not working in freezing temperatures? A lower setting is for normal weather.
Example
Dev lives in Shipley and has a Vaillant combi. He has left the radiator dial at its highest setting since the boiler was fitted. In March the house is warm but the boiler is cycling on and off.
Following Vaillant’s guidance, he turns the radiator setting down into the 60 to 70°C range, then to around 55°C once the weather turns mild. He leaves the hot water setting alone and uses the room thermostat to set the temperature he actually wants. If a room takes too long to warm up, he nudges the radiator setting back up by a few degrees. The change is made on the boiler’s own control panel, which is the user control Vaillant describes.[1]Vaillant, What temperature should my combi boiler be set at?
What people get wrong
Many people believe that a hotter boiler setting heats the house faster and is better value. Both manufacturers say the opposite on efficiency: a very high flow temperature stops the boiler condensing and can cut efficiency, and a lower setting is the more efficient one.
A second common mix-up is treating the radiator dial and the hot water dial as one setting. They control different circuits. Check your manual before changing either, because the controls and the way you adjust them differ between models.[1]Vaillant, What temperature should my combi boiler be set at?
The bottom line
The best boiler temperature setting is the lowest radiator flow temperature that keeps your rooms comfortable, and the hot water setting is a separate decision. For a modern combi, Vaillant puts the radiator figure at 60 to 70°C, falling to around 50 or 55°C in mild weather. Baxi and Vaillant disagree on hot water, so follow the manual for your boiler. If you are unsure, ask a Gas Safe registered engineer at your next boiler service.
Common questions
What temperature should my combi boiler radiators be set to?
Vaillant recommends a flow temperature of 60 to 70°C for a modern combi, because above that the boiler will not enter condensing mode. Many homes can drop to 50 or 55°C in milder months.
Does turning my boiler temperature down save money?
Baxi says turning the temperature up to maximum could cut efficiency by up to 20 per cent. Vaillant says the lower the flow temperature, the more efficient the system, and the lower your gas use and running costs.
Is the boiler temperature the same as the thermostat?
No. The boiler setting is the temperature of the water leaving the boiler. The room thermostat sets how warm you want the house. Vaillant stresses these are two separate controls.
Do the manufacturers agree on a hot water temperature?
No. Vaillant recommends around 50°C for a combi and warns that water over 45°C at the tap can scald. Baxi says not to go below 65°C to stop bacteria growing. Follow your own boiler manual.
Sources
We cite the original source for every figure: government, regulators, standards bodies and manufacturers' own documents. Each one shows the date we last checked it.
- Vaillant. What temperature should my combi boiler be set at?. Checked 11 November 2026. ↩
- Baxi. What temperature should my boiler be set at?. Checked 11 November 2026. ↩
- Worcester Bosch. Boiler not working in freezing temperatures?. Checked 11 November 2026. ↩