There is no single "right" boiler temperature, because your boiler controls up to three different things. Getting each one right keeps the house warm, keeps hot water safe and stops you paying for heat you do not need.
Three temperatures that are easy to mix up
| Setting | What it controls | Where you change it |
|---|---|---|
| Heating flow temperature | How hot the water leaving the boiler for the radiators is | Radiator symbol dial or heating setting on the boiler |
| Room temperature | When the heating switches on and off | Room thermostat, smart thermostat or app |
| Hot water temperature | How hot the water at the taps is (combi) or the cylinder is heated to (system or regular boiler) | Tap symbol dial on a combi, or the cylinder thermostat |
Turning up the room thermostat does not make the radiators hotter. It only makes the heating run for longer. If the radiators themselves feel too cool, it is the flow temperature on the boiler that decides that.
Heating flow temperature and condensing mode
Almost every gas boiler fitted in the UK in recent years is a condensing boiler. It recovers extra heat from its flue gases, but only when the water coming back from the radiators (the return) is cool enough for that steam to condense, roughly below 55°C. When the boiler sends water out very hot, the return often comes back too warm for this to happen, and the boiler runs less efficiently than it could.
That is why the usual advice for a combi or system boiler is a heating flow temperature of around 60°C or a little lower for most of the year. The radiators will feel warm rather than scorching, and the house may take a little longer to heat up, so it helps to start the heating a bit earlier. We have not quoted a saving figure here, because how much you save depends on the boiler, the radiators and the house; the principle is that cooler return water lets the boiler condense more of the time. A system that is properly balanced helps with this too, as our guide on how to balance radiators explains.
Seasonal starting points
Use these as starting points and adjust a few degrees at a time, giving the house a day to respond before changing again.
| Conditions | Heating flow setting to try | Notes |
|---|---|---|
| Mild spring and autumn days | Around 50 to 55°C | Plenty for most homes with average radiators |
| Normal winter weather | Around 55 to 60°C | Good balance of comfort and efficiency |
| Hard frost or a very cold spell | Raise towards 65 to 70°C if rooms will not warm | Lower it again when the weather eases |
If your boiler has an outdoor weather sensor fitted (weather compensation), it adjusts the flow temperature itself. Leave the installer's settings in place and ask them before overriding it.
Hot water: combis and cylinders are different
Combi boilers
A combi heats water as it flows to the tap and does not store any. Set the hot water dial to the temperature your manual recommends for your model, because the available range differs between boilers. If the shower needs a lot of cold mixing in to be comfortable, the setting is higher than you need. If the water is never hot enough even at the top setting, see our guide to hot water not hot enough.
Hot water cylinders
With a system or regular boiler, hot water is stored in a cylinder, and stored water is where legionella bacteria can grow. The Health and Safety Executive's guidance on hot and cold water systems says hot water should be "stored at least at 60°C" and distributed so it reaches 50°C within one minute at the outlets. Do not turn a cylinder thermostat below 60°C to save money.
Water at these temperatures can scald. HSE notes a scalding risk from taps above 44°C. If young children, older people or anyone vulnerable uses the bath or shower, ask a plumber about a thermostatic mixing valve rather than lowering the cylinder temperature.
How to change the settings
- Dial controls. Older and simpler boilers have two dials, one with a radiator symbol for heating and one with a tap symbol for hot water. Many are marked with numbers or dots rather than degrees, so check the manual for what each position means.
- Digital controls. Newer boilers usually have a heating button and a hot water button, each with plus and minus or a scroll wheel, and show the set temperature on the display.
- Smart controls. Some smart thermostats can set the flow temperature on compatible boilers through the app.
Only use the controls described in the user manual. Installer and service menus hold settings such as maximum output and pump speed, and changing those is a job for a Gas Safe registered engineer. The same principles apply to every brand, so the settings above suit a Vaillant, Worcester Bosch, Ideal or Baxi boiler alike.
Room temperature on the thermostat
Most households are comfortable with living areas at around 18 to 21°C. Bedrooms can usually be a little cooler. Older people and anyone unwell may need the warmer end of that range, and 18°C is widely used as the minimum for a healthy home in winter. Turn the thermostat down a degree at a time to find the lowest setting you are happy with. Our boiler thermostat guide covers where to place it and how it works with the boiler's own dial.
When a low flow temperature is not enough
A lower flow temperature works well in most homes, but not all. It can struggle where radiators are small for the room, where loft and wall insulation are poor, or on very cold days. If rooms will not reach temperature after you have bled and balanced the radiators, raise the flow temperature a few degrees. If they still will not warm up, our guide to heating on but the house cold goes through the other causes. A heating engineer can check whether a radiator is big enough for its room, and an annual service typically costs £80 to £150 if you want the settings checked at the same time.