Boiler Temperature: How to Set A Lower Combi Boiler Flow Temperature

James Elston
Written by James Elston
Updated on 2nd January 2024
Posted on 1st January 2024
Topic: Boiler Advice
Boiler Temperature: How to Set A Lower Combi Boiler Flow Temperature

How to lower combi boiler flow temperature setting advice

hot water temperature gauge

There are a number of different ways in which the efficiency of your boiler flow temperature can be increased and one of the adjustments you can make that will have one of the most significant impacts is lowering the boiler temperature.

You can find the perfect temperature for your boiler type below and how to turn down boiler temperature settings.

Using the optimum temperature will not only make your boiler more efficient but should also reduce your heating bills by between 6-8%.

In this guide, we’ll show you how to reduce the flow temperature of your boiler and also take a look at the types of boilers that allow you to do this, the best combi boiler, and give you some other very handy tips.

Got an old inefficient boiler? Check out our boiler replacement guide for energy-efficient combi boilers to see if it is time to consider a new one to keep running costs and your gas bill down. These boilers can modulate down to 10% power of their output capacity to really cut energy costs.

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Combi Boiler Flow Temperature Explained

Simply put, the flow temperature is the water temperature your boiler achieves before the water travels to the central heating system in your home and the majority of condensing gas boilers run on what’s known as 80/60 flow and return temperature range.

When a condensing boiler operates at 80/60 flow and return, the hot water temperature is 80˚c when it leaves the boiler and after it has travelled around the central heating system, it returns to the boiler at 60˚c, which is known as the return temperature.

This means that the hot water temperature has reduced because it has given off 20˚c of heat to the rooms in your home.

Most modern boilers are sold as being A-rated for efficiency, however, if a condensing boiler or best combi boiler runs at 80/60, it will not achieve A-rated efficiencies. This is because 80/60 flow and return temperatures are too high to achieve this.

When installing your boiler and heating system, many installers fail to set up the right flow temperature, which means that most gas boilers only run between 75%-85% efficiency which can mean you aren’t seeing the full affect of your boiler on your pocket.

Read our guide on how to save on your energy bills here

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Can The Flow Temperature Be Adjusted On Any Boiler?

To adjust the flow temperature on your boiler, it needs to be a condensing combi boiler as condensing combi boilers produce both your hot water and your heating.

If you’re unsure whether you have a condensing combi boiler, there are several easy ways to tell or get your Gas Safe engineer to talk you through it on your next boiler service.

  • If your boiler doesn’t use a hot water cylinder, it’s a combi boiler.
  • If it’s a condensing boiler, it will have a white pipe running to an outside or inside drain.
  • If your boiler was installed in the last 16 years, you can be sure it’s a condensing boiler.

Check out the best combi boiler right now in our guide if you want to be able to lower a boiler’s temperature for more energy-efficient heating!

Video: What is Boiler Flow Temperature & How To Turn It Down?

Check out this video where we explore boiler flow temperature. Learn why it’s essential for your heating system and get easy-to-follow steps on how to turn it down for better efficiency and comfort.

What Is The Optimal Combi Boiler Flow Temperature Setting?

Generally, the optimal flow temperature setting for combi boilers is the lowest possible temperature, and usually, the lowest flow temperature achieved in an older home is 60-65˚c, and for newer homes, it’s normally 50-55˚c.

Read more here about what temperature your hot water should be at the tap.

worcester bosch combi boiler

To operate most efficiently, your gas boiler settings and heating system must be at a flow temperature of 45˚c, however, this flow temperature can’t be achieved in many homes.

The flow temperature setting that your boiler can reach in your home depends on several different factors: the levels of insulation, how big your radiators are, and the thermostat temperature in your home.

Lower flow temperatures require radiators with larger surface areas so that the temperature inside your home still reaches the desired level. This is the same principle that would apply to an air source heat pump.

Fortunately, most modern homes have large radiators to achieve this.

As a guide, if your home was built before 2010, try setting the boiler flow temperature to 60˚c; if it was built after 2010, try setting it to 50˚c. Adjusting the central heating flow temperature shouldn’t have any negative impacts on older homes that have been modernised.

For instance, if your home has cavity walls, modern double-glazing, and good loft insulation, reducing the boiler flow temperature shouldn’t negatively affect the comfort of your home.

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How To Reduce Combi Boiler Flow Temperatures

There are several different ways that you can adjust the flow temperature on your combi boiler and heating system. This is always done using the controls attached to your boiler rather than the central heating room thermostat.


Below, we’ve provided the best settings for combi boiler flow temperate to achieve the optimum temperature, and three examples of the most common ways to reduce the flow temperature of your boiler and make your boiler even more energy efficient.


The majority of boilers come with two control dials. One dial is for controlling the flow temperature of the hot water, and the other is for controlling the flow temperature of the heating system.

To reduce the flow temperature of your heating, you need to turn the dial with the radiator icon down to the desired flow temperature. As mentioned, this will be around 60˚c for most homes.

Some boilers like Worcester Bosch boilers will have dials that use a 1-6 numbering system rather than specific temperatures. This means that the number 3 usually corresponds to 60˚c.

If your boiler uses a different system than this, you’ll need to consult the instruction manual to find out how to adjust the boiler flow temperature.

These instructions only relate to adjusting the flow temperature for your heating, not your hot water. We’ll discuss hot water flow temperatures later on.

Digital displays

combi boiler heat controls

If your boiler has a digital display, you’ll be able to view the flow temperature on the display as you adjust the radiator icon dial. Again, this won’t achieve a lower flow temperature for your heating and hot water, but only for your heating system.

Digital displays without dials

A new boiler model may have a digital display with plus and minus buttons or up and down buttons. To adjust the boiler flow temperature, you use these buttons to lower the temperature setting on the display.

You can often use the buttons to control the heating and hot water temperatures, so ensure that you only select the heating temperature option.

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If you are not quite ready for a new boiler but want to maintain your boiler’s energy efficiency see how much a boiler service cost across the UK right now or book one with Boiler Central now and your Gas Safe engineer can set the ideal temperature for your boiler for you.

What Should I Do If I Have A System Boiler With A Hot Water Cylinder?

System boilers that use hot water cylinders can’t be lowered to the same temperatures as condensing boilers, so they can’t operate at their maximum efficiency levels.

If your boiler has a hot water cylinder, it will either be a conventional boiler or a system boiler and use either an unvented or vented hot water cylinder.

system boiler hot water cylinder

Inside the cylinder, the hot water must be stored at 60˚c to destroy any legionella bacteria that might be present, as the disease can be fatal to humans. This means that the flow temperature for a hot water cylinder must be kept at 70˚c as some heat will be lost during hot water transfers to the cylinder.

Due to this, these boilers are not particularly efficient, and heat is wasted to achieve the desired room temperature. Some adjustments will need to be made to achieve maximum efficiency for these boilers.

Your boiler will need separate temperatures for the heating and hot water. To do this, you’ll need to contact a heating engineer.

As more and more households move towards low-carbon heating solutions, people will need hot water cylinders. This means adjusting conventional and system boilers to operate more efficiently will become increasingly common.

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Will I Need Help To Reduce My Boiler Flow Temperature?

Adjusting the flow temperature of your boiler should be straightforward, and if you follow the instructions we’ve given in this guide, you shouldn’t have any issues.

However, if you have any doubts about doing it yourself or suspect a boiler problem, then you should call a Gas Safe registered engineer to assist you.

If you’re struggling to work out how to adjust the flow temperature of your boiler, then it’s best to find the instructions provided by the manufacturer. This is particularly true for boilers that don’t use a numbering or temperature system for the control dials.

If you’ve misplaced the instruction manual for your boiler, then you should be able to find it online. You need to find out what the make and model of your boiler are and then search for the instruction manual in a search engine or on the manufacturer’s website.

You should also be able to call the manufacturer’s technical helpline if you’re having any issues with your boiler.

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What’s the optimal temperature for my home?

ideal temperature

The Energy Saving Trust recommends that in winter, your home’s interior temperature is between 18 and 21˚c. The World Health Organisation recommends that the ideal room temperature during the winter is 18˚c.

Both of these organizations recommend that 18˚c is the right temperature to set your thermostat to whilst you’re sleeping during the winter months.

Which is the best combi boiler to save money?

The best combi boiler to buy is the Viessmann Vitodens 050-w, due to the fact it is energy efficient and can modulate down to a ratio 0f 1:8, therefore running at an output of just 3.2kw when required. It is also equipped with a stainless steel heat exchanger therefore more reliable and longer lasting, which sets it apart from the rest of the best combi boilers that use aluminium.

How do I know if my home is ready for a heat pump?

If your central heating system and boiler can run at a flow temperature of 45˚c, you can have a heat pump fitted without your heating system needing to be modified.

Generally, if your home was built in the last ten years, has underfloor heating, or is very well insulated, then your heating system should be able to operate at 45˚c.

What changes will I notice when I lower the flow temperature?

The main change you will notice is that your radiators will feel cooler than they used to. This shouldn’t lead to your home being uncomfortably cool; if it is, you’ll need to raise the flow temperature.

You may also notice that your radiators take a little longer to heat up than they used to. This is because most boilers are set to run at much higher temperatures than they need to and tend to heat up very quickly.

This will be most noticeable for people with programmed heating systems that only turn on for a short time during the day.

So what is the correct temperature for a boiler and why it matters?

Reducing the flow temperature of your boiler is one of the easiest ways to increase its efficiency and reduce the cost of your energy bills. Although it’s more complicated if you have a conventional or system boiler, it’s still possible to achieve with some modifications.

There is minimal risk in adjusting the flow temperature of most new boilers. However, if you do have any concerns, it’s always best to contact an engineer who will be able to give you professional advice.

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Written by
James Elston
James Elston Director Of Boiler Central
Posted on: 1st January 2024
Topic: Boiler Advice

James Elston is our resident boiler replacement and heating expert here at Boiler Central. With over 20 years experience in the boiler installation industry, James ensures that he knows everything there is about our Gas Safe boiler installations, energy saving and home heating solutions. This can be from simply procuring the latest best combi boilers, to reviewing and ensuring that Boiler Central maintains the highest standards across our boiler installation company.

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