Are you considering installing a combination heating system in your home and wondering what kind of shower unit will work best with it? Or perhaps you already have a combi system and need to confirm that your planned new shower is compatible. Whatever your question, this guide will provide a better understanding of your options.
By the end of this article, you will know what a combination boiler is, how it operates, its advantages over alternatives, and which types of showers you can safely and effectively run from it.
How to Select the Right Shower for Your Combination System
Properly selecting the right shower for your home requires careful thought. The right choice ensures a consistent, warm flow of water, while the wrong one can result in an unpredictable trickle. Before focusing on the style and design of your shower, you must verify that the shower system itself is technically compatible with your hot water source. This article focuses specifically on the best options for a combination unit.
What is a Combination Boiler?
A combination boiler, often referred to as a combi system, heats water on demand rather than storing a supply of hot water.
When you turn on the hot water tap, cold mains water is drawn through the unit and heated as it passes through an internal component. The main benefits of this design are that you will not run out of hot water (provided the unit is functioning), and you only pay to heat the water you actually use. Combi systems also save space because they eliminate the need for a separate cold water storage tank or a large hot water cylinder, making them perfect for smaller living spaces.
These systems have grown immensely in popularity since their invention. They are now highly favored, with more than half of all new installations being combi systems.
How Combination Systems Differ from Alternatives
Although they are the most popular option today, not all homes use a combi system. Here are the other types you might encounter:
System Boilers
System boilers utilize a hot water storage cylinder but do not require a separate cold water tank. They contain fewer components than conventional models, simplifying installation. However, this type requires space for the cylinder and limits the amount of hot water available at any given time based on the tank’s size.
Conventional Boilers
Conventional boilers heat a tank of water when the system is activated, meaning you must wait for the tank to fill and heat up. Usage is limited by the tank’s capacity; if multiple people wanted to take a bath quickly, they would likely have to wait for the tank to refill and reheat several times.
The key advantages of combi systems over these alternatives are:
- Instant hot water and central heating.
- Compact size, making them ideal for homes with limited space.
- The potential for powerful showers, as flow is determined by the system’s output rather than gravity or position.
- Lower risk of pipes freezing.
- Easier maintenance due to fewer external pipes and components.
- No need to allocate space in an attic or loft for a water tank.
Note: Combi systems may not be the best solution if your home already experiences low mains water pressure.
What Types of Shower Are Available?
Here is a brief introduction to common shower types:
Electric Showers
Electric showers heat water instantaneously. They pull cold water directly from the mains supply and pass it over an internal heating element. An electric shower can produce hot water even if your main heating system is not working, provided it has electricity.
Standard Mixer Showers
Mixer showers allow you to control the blend of hot water (from your heating system) and cold water. You use a handle or separate controls to set your desired temperature.
Thermostatic Mixer Showers
Thermostatic mixer showers use an internal thermostat to regulate the water temperature. Once you set the desired level, the thermostat maintains it consistently, even if water pressure or temperature fluctuates elsewhere in the house.
Power Showers
Power showers include an integrated booster pump that forcibly pushes water through the system at high pressure. These are often used in areas with naturally low water pressure to provide a more invigorating flow.
Warning: Using a power shower with a combi system is generally unsuitable and may cause the boiler unit to become over-pressurized, which can be hazardous.
What’s the Best Shower to Use With a Combi System?
Showers that require a tank-fed water supply are incompatible with combi systems because combis do not store water. This effectively rules out traditional power showers, as the combi system can only produce hot water at a fixed rate, and pumping cannot increase that rate.
The general guideline is that any shower whose mixing valve is compatible with a combi system can be used.
Here are additional factors to look for:
- A hot water pipe with a diameter of around 15mm is typically suitable for combi systems. If your pipes are larger, you can use reducing fittings to ensure compatibility.
- To guarantee an uninterrupted warm shower, your combi system should ideally be able to heat 12–15 liters of water per minute.
- Thermostatic mixer valve showers are highly recommended for use with combi systems.
Thermostatic valves excel because they can compensate for any sudden variations in water temperature or pressure that may occur in the mains supply, providing a consistent and stable shower experience. For example, if someone turns on a hot water tap downstairs, a thermostatic valve will prevent the shower water from suddenly becoming scalding hot or freezing cold. If you choose a non-thermostatic mixer, it is best to shower only when no other hot water fixtures are in use to maintain a stable temperature.
Electric showers also work well with combi systems, though they are not always considered the premium option. A distinct advantage is that an electric shower will continue to provide hot water even if your main heating system were to fail.
For total confidence in your choice, it is always recommended to consult with a qualified professional to select the best shower for your specific home setup.
Troubleshooting Combi System Showers
Here are some common issues you might encounter with a shower running off a combi system:
Water Not Hot Enough
If your mains water pressure forces water through the shower unit faster than the combi system can heat it, you will struggle to reach or maintain your desired temperature.
In this scenario, you could switch to an electric shower, which handles the heating independently. While upgrading your combi system to one with a higher output rating would also resolve this, it is a drastic and costly solution. Be aware that if your combi system is too powerful for your home’s actual demands, it may begin “short cycling”—quickly reaching maximum capacity and then shutting down.
Water Temperature Fluctuates
If your shower temperature varies unexpectedly, it might indicate that your mixer valve is incompatible with your combi system. Alternatively, it could mean the hot and cold water connections were installed incorrectly.
Fluctuations can also occur if the combi system’s preset temperature valve is kicking in. These valves are often factory-set around 43 degrees Celsius to prevent scalding. You should check and investigate the unit’s preset temperature settings.
If you are unsure how to diagnose or fix a problem, contact the helpline provided by the manufacturer or speak to a qualified professional.
Conclusion
This guide provides a comprehensive overview of the showers compatible with your combi system. Whether you are moving into a home with this system or planning an upgrade, you should now have the information necessary to confidently choose the perfect shower for your bathroom!
