Best Showers for Combi Boilers

Close up image of a man adjusting the settings on his combination boiler
Published: 10th January 2020
Author: Des Roberts

Are you thinking of installing a combination boiler in your bathroom, and wondering what sort of shower you can run off it? Or perhaps you have a combination boiler already, and you want to make sure the new shower you're planning to get is compatible. Whatever your question, this guide will help you gain a better understanding of your options.

By the end you'll know what a combination boiler is, how it works, the benefits compared to alternative options, and which types of shower you can safely run from one.

How to Choose the Right Shower For Your Combination Boiler

There are a few things to consider when choosing the right shower for your bathroom and it is important to take the time to decide properly. Choosing the right shower is the difference between a rich, warm flow of water and an unpredictable trickle. Take it from us: no one likes to shower under an unpredictable trickle. Before you think about the style and design of your shower, you need to make sure the shower system itself is suitable for your boiler. This article focuses on the best shower for a combination boiler, so we will begin by introducing those.

What is a Combination Boiler?

Close up image of a man adjusting his combination boiler

A combination boiler, or combi boiler, as we will be referring to them from this point onwards, heats water as and when you need it rather than storing hot water.

When you turn on the hot water tap, cold water is pulled through the boiler and heated up as it travels through. The main benefits of this is that you will never run out of hot water as long as the boiler is functioning properly, plus you only pay for the hot water you use. They also take up less space thanks to the fact that you do not need a cold water tank or hot water cylinder, making them perfect for smaller living spaces.

Since 1868, when Benjamin Maugham created an invention resembling the combi boiler we know today, they have only increased in popularity. British Gas have dubbed the combi boiler "The UK's most popular type of boiler" based on the ratio of boilers they install and with good reason. Today, more than half of new boiler installations are combis.

How Do Combination Boilers Differ From the Alternatives?

Despite being the most popular option, not all homes have a combi boiler. Here are the other types you might come across:

System Boilers

System boilers have a hot water storage cylinder, but no water tank and contain fewer components than other types, facilitating quick and easy installation. This type of boiler needs a bit of space for the cylinder and limits how much hot water you can use due to the size of its tank.

Conventional Boilers

Conventional boilers heat a tank of water when you switch the hot water on, meaning you have to wait for the tank to fill up. You are also limited by the size of the tank. If a few people wanted to have a bath in quick succession, it is likely that you would have to wait for the tank to fill up a couple of times.

The main takeaways when considering the benefits of combi boilers versus alternatives are as follows:

  • Instant hot water and central heating.
  • Small, meaning they are ideal for homes with limited available space.
  • Powerful showers, because flow is determined by the boiler rather than its position.
  • Lower risk of pipes freezing.
  • Easier maintenance, thanks to fewer pipes.
  • No need to find space for a water tank in your loft.

Bear in mind that combi boilers may not be the best option if you have low water pressure in your home.

What Types of Shower Are There?

We will briefly introduce these, in case you are not already familiar:

Electric Showers

Cut out image of an electric shower with accompanying riser rail set

Electric showers heat water instantly, by pulling cold water from the mains and over an internal heating unit. An electric shower will be able to produce hot water regardless of whether your boiler is working, as long as it is receiving electricity.

Standard Mixer Showers

Mixer showers give you control over the mixture of hot and cold water. You use taps or a handle to set the temperature just where you like it.

Thermostatic Mixer Showers

Product Lifestyle image of the Keuco IXMO Chrome Square Shower Set with Slide Rail

Thermostatic mixer showers use a thermostat to regulate temperature. Just set the level you want and the thermostat takes care of the rest, giving you a consistent flow.

Power Showers

Power showers have an inbuilt booster pump that forces water through the system at high pressure. This is useful in low-pressure areas, to help you avoid the unpredictable trickle we mentioned earlier.

Take note: A power shower may cause your unit to become over-pressurised, which can be dangerous. Our recommendations are based around making shower time as safe and pleasurable as possible.

What’s the Best Shower to Use With A Combi Boiler?

Showers that require tank-fed water flow are unsuitable for combi boilers, because they do not have a tank. Unfortunately this rules out power showers, because the combi boiler can only produce hot water at a fixed rate. Pumping, no matter how hard, cannot change that.

The rule of thumb is that any shower whose shower valve is compatible with a combi can be used with one. There are some other things to look out for too:

  • A hot pipe of around 15mm diameter is suitable for use with a combi boiler. If it is much bigger than that, you can use reducers to bring the size down and make it compatible.
  • To ensure your warm shower is uninterrupted, your combi boiler should be able to heat 12-15 litres of water per minute.  
  • Thermostatic mixer valve showers come highly recommended for use with combi boilers.

In fact, someone over at the Screwfix support forums had this to say: "If the hot water flow rate of your boiler is enough to meet the requirements of the mixer then I cannot think of a reason not to use a mixer." This is because the valve is able to control for any variations that may occur in the temperature of the water, meaning you get a consistent and perfectly heated stream of water to shower under.

You may be wondering what this means in practice. Well, if someone downstairs turns the hot water on to wash up, your thermostatic valve will prevent the water suddenly getting scalding hot or freezing cold (two things people usually like to avoid). If you go for a non-thermostatic mixer, try to shower when hot water is not being used elsewhere in your home if you wish to achieve a consistent temperature.

Electric showers work well with combi boilers too, although they aren't considered the best option. An electric shower will keep working if your boiler were to fail, thanks to the water being heated by the shower system itself.

For complete peace of mind, we recommend speaking to a professional about choosing the best shower for your home. While this article provides plenty of generalised information, there may be factors specific to your home that influence your options.

Troubleshooting Combi Boiler Showers

Here are some problems you may come across with a combi boiler shower.

Water Not Hot Enough

Image a woman shocked by the temperature of the water from her shower

If your water pressure if feeding water through your shower faster than it can be heated, you will struggle to reach or maintain desired temperatures.

In this instance, we would recommend that you switch to an electric shower which will heat the water itself. Upgrading your combi boiler to a stronger power rating would similarly resolve this issue, however we would advise that this option is quite drastic. If your boiler is too powerful for the demands of your home, it may begin short cycling, which means it will quickly reach maximum capacity before simply shutting down. 

Water Temperature Fluctuates

If your water temperature is fluctuating while you shower, this might mean that your mixer valve isn't compatible with your combi boiler. Alternatively, this could be an indication that the hot and cold connections are installed the wrong way round.

This can also happen when the boiler automatically turns off the hot water once a certain temperature is reached. Investigate the preset temperature valve to determine if this is the case. Usually these are set around 43 degrees celsius to prevent scalding.

If you are unsure how to fix something, ring the phone number on your boiler, or talk to a qualified professional.

In conclusion…

There you have it: a rundown of showers that are suitable for use with your combi boiler.

If you have moved into a home with a combi, or are planning to replace your existing boiler with one, you should now have the peace of mind to choose the perfect shower for your bathroom!