Optimum Temperature Setting For A Combi Boiler

The ideal hot water temperature for a combi boiler is different for everyone but there are certain minimum and maximum temperatures we should be sticking to that are safe. It will also keep the energy bills down.

What is the best temperature setting for a combi boiler?

You should set your combi boiler to a temperature between 50°C and 60°C for the highest efficiency. This temperature is sufficient allows for an adequate supply of hot water while also reducing the risk of scalding. The optimum temperature setting for central heating is typically around 70-75°C. This temperature setting effectively heats the home while reducing energy consumption.

Setting the temperature lower than 50°C increases the risk of legionella disease.

It is important to note that the specific temperature setting may vary based on the specific model of combi boiler and the individual needs of the household. It is recommended to refer to the manufacturer’s guidelines or consult a professional for the recommended temperature setting for your specific combi boiler.

The Health and Safety Executive recommends a discharge temperature of between 35-46ºC so it doesn’t cause scalding but a higher storage temperature of 60ºC to prevent Legionella bacteria.

hot water temperature setting

Here we look at the main factors for the best hot water temperatures.

How to adjust your hot water temperature

When you change the temperature to between 50 and 60 degrees, you want to be able to run a hot bath or sink without having to mix it with cold water. With a combi boiler, this is as simple as adjusting the setting on the front control panel which shows the tap symbol.

If you have a hot water tank, you can adjust the thermostat at the side of the tank so you are not overheating your hot water, the ideal temperature would be 60 degrees.  Make sure your tank is insulated as well to save you money by stopping the heat loss from the tank.

What is the most efficient hot water temperature setting?

When it comes to efficient use of hot water in the home, we will look at the temperature in the radiators also.

One of the simplest things you can do to save money is by controlling your combi boiler hot water temperature and adjusting this could save you up to £40 per year.  For combi boilers, the recommended output temperature for the radiators is 75°C. 

The higher this temperature is set, the quicker your boiler will be able to heat your home. However, you may find that your heating bills increase and your boiler’s efficiency could decrease by around 10 or 20%.

While radiators will get hot quicker if the boiler thermostat is set at a higher temperature, the boiler may not condense, which will also reduce its efficiency and cost you more money in bills.

what temperature should hot water be set at combi boiler?

According to the HSE, set the hot water temperature between 50-60°C. This setting should provide an ideal balance of efficiency and comfort. Anything above 45°C can scald the skin and must be mixed with cold water. For most homes, 55°C tends to be the ideal temperature setting.

For condensing boilers, it is important to set the temperature at 55°C or lower because only then will you benefit from the better efficiency these boilers can provide. The dew point – the temperature at which water starts to form in the heat exchanger, can only be reached when the water temperature is 55°C or lower. The lower it gets the more efficient the condensing boiler will be.

Legal temperature for hot water

According to the Health and Safety Executive, hot water should be stored at least at 60°C and distributed so that it reaches a temperature of 50°C within one minute at the outlets. 

The objectives are to store water at above 60ºC if you have a storage tank, distribute water at 55-60ºC, yet deliver water at discharge temperatures between 35-46ºC.  This is to prevent the risk of Legionnaires’ disease.

Legionella risk in water

Legionella bacteria is commonly found in water. The bacteria multiply where temperatures are between 20-45°C and nutrients are available. The bacteria are dormant below 20°C and do not survive above 60°C. The primary method used to control the risk from Legionella is water temperature control. 

Legionella bacteria thrives at temperatures between 20°C and 45°C so one of the key control measures for minimising the risk is to ensure that your cold water is cold (i.e. below 20°C) and the hot water is hot (above 50°C).

How to check the water temperature

Turn the hot tap on and leave it running for about 30 seconds, then fill a measuring jug or anything that won’t lose heat quickly.  Dip in a suitable thermometer and note the temperature.

When doing this for the first time, the tap furthest away from the boiler should be chosen, or the bath tap where the ideal temperature will be required.  You can adjust the temperature up or down to suit.

How to adjust hot water temperature on a combi boiler

Combi boilers have two separate temperature controls: one for the tap and one for the radiator, with a symbol of each one. Adjust the temperature of the tap control slightly, either by turning the dial nearest to it up or down, or, on newer boilers pressing the plus and minus button until you reach the desired temperature. Test the hot water again.

hot water tap temperature check image

Scalding risk with hot water 

There is a risk of scalding where water comes out of taps at temperatures above 44°C especially for the very young, elderly people, and people with disabilities or those with sensory loss who may not be able to recognise high temperatures and respond quickly. 

The temperature at the tap is normally 55⁰C but is made to a comfortable temperature when you mix cold water with it, otherwise you will easily get a burn.

The Department of Health recommends the temperature for bathing should be no higher than 43oC and showering at no higher than 41oC. For babies, the temperature should be no higher than 37oC.

When running a bath always put the cold water in first and then bring it up to the required temperature, rather than the other way round.