What Temperature Should My Boiler Be Set At For Hot Water UK

Last updated: January 19, 2024

What is your boiler’s flow temperature? And how can changing it help you save more money on your heating bills? In this guide, we’ll explain boiler temperature settings and how to optimise them for efficiency.

The temperature of the water in the supply pipe, commonly referred to as the flow pipe, in a heating system is called boiler flow temperature – this is also often referred to as the boiler’s radiator heating temperature.

The correct boiler flow temperature is essential to obtain optimum efficiency from the boiler.

In fact, a recent report from the Heating and Hot Water Council (HHIC) suggests that households can save 6.4% to 8% energy by reducing the heating system to the mean flow temperature of 50°C on their condensing combi boilers. 

The reality is that most boilers run 10% to 25% under their A-rated efficiency due to the higher flow temperature.

The optimum flow temperature not only reduces your energy consumption, but significantly increases the boiler efficiency.

So, how do you take advantage of these combi boiler settings for your own home?

To understand and learn how, first, we need to understand how flow temperature works and how to control it.

Correct Condensing Boiler Temperature Settings

Central Heating Boiler Temperature Settings

Below we’ll explain how to optimise your boiler’s flow temperature and how changing your units boiler temperature settings can work to potentially save you up to 8% on your energy bills.

What is flow temperature & how does it work?

Flow temperature is simply defined as the temperature your boiler heats the water to before delivering it to your radiators.

Most new boilers have a standard 80/60 flow and return temperature which means that a flow temperature of 80°C is sent to the radiators of your home.

After travelling through all the radiators of your house, it sends back 60°C water to your heating system while giving 20°C to the house.

Yet, this standard flow temperature too high to achieve the A rating efficiency that is advertised on modern combi boilers.

In order to make your combi boiler activate condensing mode, the flow temperature needs to be reduced.

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The gas combi boiler will only start to operate in condensing mode at 70/50°C. Additionally, only when the flow temperature is at 60°C or lower will the boiler recover enough heat attain maximum efficiency.

What type of boiler do I need? 

The vast majority of UK households have gas condensing combi boilers. If you have one then you can control the flow temperature on your boiler.

A combi boiler is able to provide both heating and hot water under a single unit. All the boilers fitted in the last 16 years are condensing boilers, i.e. after 2005.

You can tell if you have a condensing boiler by looking underneath your combi boiler – if there is a plastic pipe coming out, then it’s a condensing unit.

This was a result of Boiler Plus Legislation, which essentially outlawed the sale of non-condensing boilers.

What is an ideal boiler flow temperature? 

Setting boiler flow at a high temperature can increase your bills considerably while decreasing your boiler efficiency by between 10% to 25%.

The optimum flow temperature helps to increase the boiler efficiency while keeping your house warm and cosy. 

Ironically, condensing gas boilers are designed to achieve 92% efficiency, but this cannot be obtained if the flow temperature is set at 80/60.

To get the 92% efficiency from your combi boiler, you must set the flow temperature low, allowing it to run on condensing mode as much as possible.

In other words, the boilers are not automatically A-rated out of the box – they need to be set so that they can perform at the optimum level of boiler efficiency.

The recommended boiler output temperature for heating or radiators is 75°C and for hot water, it is between 50°C to 60°C.

How do I reduce boiler flow temperature?

The boiler flow temperature should not be confused with the room thermostat.

The temperature you will set on your combi boiler will not be the temperature of your room.

Typically, you can adjust your flow temperature from the front of your boiler. 

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The display and the way of boiler settings are not the same in different brands. Let’s have a brief look at these.

How-To-Reduce-Boiler-Flow-Temperature

Changing your boilers temperature settings:

Boilers with dials: 

Most combi boilers come with dials, one for heating and the other for hot water.

Some boilers also come with only one dial which is meant to control heating flow temperature. The dials are either numbered or have dashed lines.

The flow temperature in most boilers operates between 30°C to 80°C.

If you work it out manually, 55°C will be halfway which will be number 3 on a dial that has numbers from 1 to 6.

Some boilers have ‘e’ on the dial which stands for economy. If you’re setting your boiler to use the economy mode, you are typically setting it to operate at 65°C. 

Heard about the gas boiler ban and wondering what the alternatives to gas boilers are? Read our complete guide to replacing your gas boiler with a heat pump.

Dials with digital display: 

Some boilers have a digital display which shows the setting you are in.

Whatever setting you choose will appear on the screen which makes it easier to adjust the flow temperature.

In this case, turn the dial down until you reach 55-60°C. 

Digital display with buttons: 

The new boilers came up with the addition of the digital display boilers by introducing up and down buttons which makes the adjustment of flow temperature and hot water even easier. 

Best boiler temperature settings for a condensing boiler to condense

A condensing boiler recovers all the heat from the flue gases and uses it to heat your home. This makes it the most efficient type of boiler.

To help it work efficiently, the heat exchanger needs to be equal to or below the dew point temperature. 

A measurement that determines the humidity of air is called dew point temperature. It is the temperature at which water droplets form in the heat exchanger.

The ideal dew point temperature for a gas boiler is around 55°C or lower.

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In simple terms, the water in the return pipe must be 55°C or lower otherwise your boiler will not perform at maximum efficiency and will not condense.

Newer boiler models will come with a useful icon on the screen that shows you the point at which the condensing mode will be turned on.

This new innovative feature put the guessing game to an end with users just having to turn the dial towards the marked point.

What if I have a hot water cylinder?

Unfortunately, the boilers with a hot water cylinder are not efficient.

According to the Centre for Sustainable Energy (CSE), a domestic hot water cylinder thermostat should be set at 60°C to 65°C.

The higher thermostat will increase the risk of scalding as the water that comes out of the taps will be too hot. Installing a mixing valve for extra safety is a good idea.

CSE suggests that setting the thermostat to a high temperature will not help speed up the heating up of water.

It will simply mean that you have to add lots of cold water to the hot and will have wasted the energy spent in raising it to an unnecessarily high temperature. 

Can I set my thermostat lower than 60 degrees? 

Lowering the thermostat from 60°C in the water cylinder will not increase its efficiency but will increase the risk of contracting Legionnaires disease.

This is a form of pneumonia that’s caused by bacteria in water if the temperature of the water in your cylinder is not hot enough. 

How old is your boiler? Should you consider a boiler repair or start looking at the latest boiler prices? It’s no secret that boiler efficiency deteriorates over time.

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