Boiler Settings That Can Save Energy: Flow Temperature and Controls
Many gas boilers are installed with settings that favour speed over efficiency. A few careful adjustments can help a modern boiler work closer to its best. This guide explains the idea in plain terms. If you are uncomfortable changing settings, ask a Gas Safe registered engineer to do it for you.
How a condensing boiler saves energy
Modern boilers are condensing boilers. They capture extra heat from the exhaust gases by cooling them until water vapour condenses. For this to happen, the water returning to the boiler from your radiators needs to be cool enough, in practice below about 55°C. When the return water is hotter, the boiler still works but does not condense as much, so it is less efficient.
Lowering the flow temperature
The flow temperature is the temperature of the water the boiler sends to your radiators. Many boilers are set to 75°C or higher out of the box. Government-backed advice, such as that from the Energy Saving Trust, suggests that lowering it, often to around 60°C or below, helps a condensing boiler run more efficiently. In a well-insulated home, rooms still reach the temperature you want, but the radiators run a little cooler and the heating stays on longer.
Try it gradually. Lower the setting, live with it for a few days, and raise it slightly if the house does not warm up enough on the coldest days. Some boilers have a weather compensation feature that adjusts the flow temperature automatically.
Do not change your hot water setting carelessly
The domestic hot water setting on a combi boiler is separate from the heating flow temperature. Lowering hot water temperature too far can create a risk of legionella bacteria in stored water systems, so follow the manufacturer's and your installer's advice, especially if you have a hot water cylinder.
Use your controls properly
- Programmer or timer: heat the home only when needed. Set it to come on shortly before you get up and switch off when you leave or go to bed.
- Room thermostat: set it to a comfortable temperature, and avoid turning it up higher for a faster warm-up, because the boiler does not heat faster that way.
- Thermostatic radiator valves (TRVs): use them to set different temperatures in different rooms, for instance a cooler bedroom.
See our guide to smart thermostats and heating controls for more.
Keep it serviced
An annual service by a Gas Safe registered engineer keeps your boiler safe and efficient. Check the registration on the Gas Safe Register website before work begins. Fit a carbon monoxide alarm, and learn the symptoms of poisoning, which include headaches, dizziness and nausea.
Know when it is time to replace it
If your boiler is old, repeatedly breaking down or very inefficient, upgrading may make sense. See when to replace your boiler.