Is your boiler running hotter than it needs to?

There are two temperature settings in most oil-heated homes, and people tend to confuse them.

The room thermostat decides when the heating comes on. The boiler flow temperature decides how hot the water is when it leaves the boiler for the radiators. That second dial is often left at the factory setting, which is usually somewhere around 75 to 80°C. For many houses that is hotter than the radiators need.

Why lower is cheaper

A lower flow temperature does two things. The boiler loses less heat through the pipework, and, if it is a condensing boiler, it spends more of its time in condensing mode, where it recovers heat from the flue gases that would otherwise go up the chimney. Most oil boilers fitted since 2007 are condensing models. The label on the front or the installation manual will tell you.

The radiators run a little cooler, so the house takes slightly longer to warm up, but it reaches the same temperature. The thermostat still switches the heating off at the point you set.

What to try

1. Find the flow temperature dial on the boiler. It is usually marked with a radiator symbol or a range of numbers.
2. Turn it down in small steps, say 5°C at a time, and live with each setting for a few days.
3. If a room stops reaching the temperature you want on a cold day, go back up one step.

Somewhere around 60 to 65°C works for a lot of homes with reasonable insulation. Older, draughtier houses may need more.

One thing to keep hot

If you have a hot water cylinder, its own thermostat should stay at 60°C or above. That is the temperature that stops legionella bacteria growing in stored water, and it is separate from the radiator setting. If your boiler uses a single dial for both heating and hot water, or you are not sure which is which, ask your heating engineer to set it up at the annual service rather than guessing.