combi boiler temperature settings

Optimum Combi Boiler Temperature Settings: Complete Guide

Last updated on June 8th, 2024

Looking for the best combi boiler temperature settings for your home?

Having your temperature settings too high can waste a lot of money, especially with the ridiculous price increases in the UK recently.

Having them too low is good for your bank balance, but probably not good for your comfort.

A large combi boiler can cost a lot more to run when the temperature is too high.

As a heating engineer, I will tell you the most efficient combi boiler temperature settings to help keep things cosy, but also keep the gas bill down as much as possible.

Combi Boiler Heating Temperature Setting

The optimum heating temperature to set your combi boiler to is different to the optimum temperature you set the combi boiler thermostat to.

These two are separate temperatures, which are often confusing for homeowners.

What’s the Optimum Temperature to Set a Combi Boiler?

It varies, you can get large and small combi boilers, different system setups etc, but for most combi boilers, the optimum temperature to set your combi boiler to on the heating is 65 °C.

the optimum temperature to set combi boiler

If your home doesn’t heat up quickly enough, then turn it up. If the radiators are too hot to touch, and you don’t want the kids or pets to burn themselves, then turn it down a bit.

The optimum thermostat temperature for most people is normally 20 or 21 °C. This totally depends on your personal comfort zone, but the lower temperature you can handle the better.

How to Set the Flow Temperature on a Combi Boiler

How to set the heating flow temperature setting on a combi boiler is very straightforward.

On most combi boilers, there are usually two dials, (sometimes only one), and one will have a radiator icon for the heating.

Turn this dial until you reach the desired combi boiler heating temperature setting.

how to set the flow temperature on a combi boiler
Setting the flow temperature

If there are no actual temperature numbers, having it set to around two-thirds of the maximum is normally the best flow temperature to set it at. Or set it to E if there is one there.

If you don’t have any dials to turn, then you will have buttons. You will need to press the buttons up or down to set the flow temperature you want.

You might have to check the combi boiler manual if you are struggling to work it out.

Combi Boiler Hot Water Temperature

It really doesn’t make much difference when it comes to gas usage the temperature the hot water should be set at, as it is not really on for prolonged periods of time, unlike the central heating.

Most showers and taps mix the hot and cold water so it’s best to have the hot water temperature set too high at the boiler rather than too cold.

You can turn the temperature down at the tap or shower if it’s too hot but you can’t turn it up if it’s not set high enough at the boiler.

What Temperature Should Hot Water be Set at Combi Boiler?

The standard for what temperature hot water should be set at is around 55 °C. If this is not hot enough, then turn the hot water temperature up. Too hot? Turn it down.

temperature hot water should be set at on a combi boiler
The temperature hot water should be set at

Combi Boiler Hot Water Temperature Too Hot

If your combi boiler’s hot water temperature is too hot for you, then the first thing you need to try is to turn the temperature down at the boiler.

This could be a dial on the boiler or could be a button depending on which combi boiler you have.

You might have to check the boiler manual, as some combi boilers can be overcomplicated for such simple things as adjusting the hot water temperature setting.

Boiler Problems

If changing the temperature on the combi boiler does not change the temperature of the water coming out of the taps, then you have a problem, and you should call a heating engineer.

It’s impossible to know what the problem could be without looking at it, but it could be:

  • The plastic spindle on the temperature dial is broken
  • The teeth that hold the spindle are worn down
  • The temperature sensor is faulty

It could also be something more serious like needing a new circuit board, amongst other things.

Combi Boiler Hot Water Temperature Fluctuates

If your combi boiler’s hot water temperature fluctuates, then there is a problem with the boiler or the water supply, and you will need a combi boiler repair engineer to have a look.

How to Use Combi Boiler Efficiently

If you do not have a room thermostat, then you should definitely get one. Having your heating on without anything to control the temperature is a bad idea.

The combi boiler heating temperature controls the temperature of the radiators, the room thermostat controls the temperature of the room that the thermostat is in.

Hive room thermostat being set
Hive room thermostat

The hotter you set the heating temperature to on the combi boiler, the hotter the radiators are to touch, and the quicker the room temperature will heat up.

  • If the room thermostat is set at 20 °C, the room thermostat will turn the heating off when the temperature in that room reaches 20 °C.
  • When the temperature drops below 20 °C, the heating will come back on to keep it at 20 °C.
  • The hotter the temperature is set to on the combi boiler, the quicker the room will reach 20 °C, but it will never be more than 20 °C, even if set to 80 °C on the combi boiler unless you change the temperature on the thermostat.

Having your combi boiler heating temperature set to the maximum will help heat your home up quicker. It will also cost more money for gas, especially if you have a condensing combi boiler as it will not condense if it’s too hot.


Getting your combi boiler temperature settings right is more important than ever with sky-high gas prices.

If you have thermostatic radiator valves on your radiators then you could turn some down in the rooms that don’t get used much. This will save on gas usage.

Having your radiator temperature at that right balance of not too hot and not too cold is crucial in the winter.

Feel free to ask me any questions in the comment section below and I’ll try my best to help.

Please share this post if you find it helpful.


Should radiators be too hot to touch?

Radiators can be too hot to touch and quite often are. If you have small children in your home regularly, then having the radiators too hot to touch is probably a bad idea.

You can turn the temperature of your radiators down at the boiler by turning the dial with the radiator symbol down or you might have to press a button.

Why are some of my radiators hotter than others?

Some of your radiators are hotter than others most likely because you need to balance the radiators.

You might need to flush your central heating system also, but most of the time when some radiators are hotter than others it’s down to them needing balanced.

Does turning boiler temperature down save money?

Yes, turning the boiler temperature down will definitely save money.

Whether it’s turning the room thermostat down (which will mean the boiler isn’t on as much) or turning the radiator temperature down on the boiler (which means the boiler won’t be working as hard) both ways will save gas and therefore money!


  • Steven Reid

    I am a full-time plumber and Gas Safe registered engineer. I incorporated Housewarm Ltd. in 2011 to provide heating and plumbing services to homes in Newcastle upon Tyne, England. I now blog about what I've learned over the years to help DIYers and plumbers.

    View all posts
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6 thoughts on “Optimum Combi Boiler Temperature Settings: Complete Guide”

  1. Vanessa Steffen

    I have tried adjusting and resetting my water temperature on my boiler but for the last several days it’s showing as 20° and switches in when u reset it but it won’t go any higher despite being set to 65°. What should I do?

  2. uwidavid

    When I set the radiator temperature say to 50°C using the up/down buttons. The displayed temperature (and I presume the radiators) are much hotter 70-80 °C. Why is this? The temperature sensor is working as it is giving a (too high) reading so why does the “software” not turn down the heat? It is a Baxi combi 124-128.

    1. Steven Reid

      Yeah if you’ve set the heating temperature setting to 50 and it’s actually 70+ then you have a problem. Potentially gas valve or PCB.

      1. uwidavid

        I’ve figured it out. The numbers that come up when I press the “radiator buttons” is actually a temperature profile (based on the external temperature) not the boiler temperature. So if it’s minus outside almost ant setting will take the radiators up to 85° . Why do these things have to be made so difficult?

        1. Steven Reid

          The temperature setting controls are definitely getting more complicated and annoying on some boilers and thermostats, I think it’s down to trying to make them as energy efficient as possible.

          1. uwidavid

            Maybe as they have put a microprocessor in there and employed a software engineer. They need to think of new and exciting things to add to what should be a basic function device.

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