What Temperature Should Your Boiler Be Set At?

On a combi boiler, set the heating dial to around 60°C or slightly lower and the hot water dial to about 50°C. That's the short answer for most London flats and houses. Many boilers are left on 70 or 80°C from the day they were installed, which keeps a condensing boiler from condensing and burns more gas than necessary. If you have a hot water cylinder, the advice is different, because stored hot water needs to reach 60°C. With the heating season starting, now is a good time to check both dials.

The two dials on a boiler

Most combi boilers have two controls, either knobs or buttons on a display:

• Heating, often shown as a radiator symbol. This sets the flow temperature: how hot the boiler heats the water before it goes round the radiators.
• Hot water, often shown as a tap symbol. This sets how hot the water is at your taps and shower.

Neither dial sets how warm your rooms get. That's the job of the room thermostat and the thermostatic radiator valves. Turning the boiler up doesn't warm the house to a higher temperature; it just makes the radiators hotter so the house gets there faster, at the cost of efficiency. Our guide to how thermostats work explains the difference.

Heating (flow) temperature: about 60°C

Modern gas boilers are condensing boilers. They recover extra heat from the flue gases, but only when the water coming back from the radiators is cool enough for the water vapour in those gases to condense. According to Nesta's Money Saving Boiler Challenge, combi boilers work best at a flow temperature of 60°C or below, while most UK boilers are set much higher, often 70 to 80°C. At 60°C a combi runs in condensing mode.

The campaign says the change cuts gas use for the average combi household without affecting hot water. The trade-off is that radiators run cooler, so rooms take a little longer to warm up. Most people don't notice once the heating comes on half an hour earlier.

Some newer boilers also have weather compensation or load compensation, where the boiler adjusts the flow temperature itself based on the outdoor temperature or how hard it's working. If yours has it set up, leave it to do its job.

Hot water temperature on a combi: around 50°C

On a combi, water is heated as it passes through the boiler, so nothing is stored and there's no legionella concern from a tank. Around 50°C is comfortable for showers and washing up, and lower settings reduce the risk of scalding, which matters with young children or older relatives in the house. Turning the heating dial down doesn't affect the tap temperature on a combi.

If your hot water is running lukewarm even with the dial turned up, the setting isn't the problem. See our guides to no hot water in the shower and no hot water when the heating works.

System and regular boilers with a cylinder

If you have a hot water cylinder, the rules change. HSE guidance on legionella is that stored hot water should be heated to 60°C. On many system and regular boilers the same flow from the boiler heats both the radiators and the cylinder coil, so turning the flow temperature right down can stop the cylinder reaching a safe temperature. The Money Saving Boiler Challenge doesn't give advice for homes with a tank for this reason.

In practice, leave the cylinder thermostat at 60°C and get a heating engineer to check whether your controls allow the heating flow to be lowered separately. If you're not sure which system you have, our guide to types of central heating systems will help you tell.

How to change the setting

You're only changing the user controls on the front of the boiler, which the manufacturer intends you to do. Never open the casing; anything inside must be done by a Gas Safe registered engineer.

Cold snaps and rooms that won't warm up

A lower flow temperature works for most homes most of the time, but not every day of the year. In a hard frost, a draughty Victorian house or a flat with small radiators may not reach temperature at 60°C. It's fine to turn the heating dial up for those spells and back down afterwards.

If rooms struggle at 60°C in normal autumn weather, though, the boiler setting is usually covering up another problem:

• Radiators cold at the bottom point to sludge. See signs your radiators need a power flush.
• Some radiators hot and others lukewarm means the system needs balancing. See how to balance radiators.
• Radiators cold at the top need bleeding, then a pressure check.
• TRVs stuck or set too low in some rooms. See TRV settings explained.

For a full pre-winter routine, see when to turn the heating on, and what to check first. If your controls are old or confusing, our heating controls page covers upgrades, and our central heating repair team can find out why rooms won't warm up. Labour is £95 an hour, the £60 call-out is waived when the job runs over 2 hours, and we confirm the price before we start.

Frequently Asked Questions