Flushing Out Legionella with Hot Water Circulation Pumps

Legionella. What is it? Where is it found? How can it be prevented? These are just three of the most asked questions we hear and given the seriousness of some recent cases, who wouldn’t be concerned?

One certainty, however, is that the days when flushing taps was considered enough to stop the spread of Legionnaires’ disease in homes and commercial properties are now a distant memory. Fortunately, there are several preventative measures that can be taken to protect pipework and safeguard a home or building’s water supply.

Before diving into these, it’s important to understand what Legionella actually is and where it can be found.

A lecture on Legionella

Legionella is a type of bacteria that can grow in commercial and domestic hot water systems. When breathed in, it can cause Legionnaires’ disease, a potentially fatal form of pneumonia. Mild outbreaks, which often go unnoticed, can present symptoms similar to those of a cold or flu.

Places where the bacteria can be found within a hot water system’s equipment, pipework and outlets, include showerheads, taps and hot water cylinders – essentially anywhere water can stagnate. Especially, Legionella will thrive if:

• Water temperatures are between 20°C and 45°C
• There are dead legs in the system (this is where water rarely or no longer flows through sections of pipework)
• Water flow is poor

Simple solutions

Rest assured, as a few straightforward measures can significantly reduce the chances of Legionella spreading.

Start by checking for dead legs and then removing these from a plumbing system. Dead legs occur when a plumbing system has been modified, and due to the changes, sections of pipework become isolated from water flow. Because of this, water in these pipes can become stagnant, creating a perfect environment for Legionella to grow.

While they can be difficult to spot, particularly in properties which have been added to or modified over the years, dead legs should ideally be cut off entirely rather than just being capped off. The latter can still allow water to stagnate inside the pipe, meaning the risk of bacterial growth continues to linger. If removal isn’t possible, these pipes should be flushed regularly to prevent stagnation. Did you know that even a dead-leg of 25mm in length can harbour harmful bacteria?

Insulating pipes can prevent the growth of Legionella, as this will help avoid heat losses and maintain water temperatures outside of the 20°C and 45°C range where it thrives. It’s simple – keeping hot water hot and cold water cold so that there are consistent temperatures throughout the system, ensuring water doesn’t cool down or heat up when it shouldn’t. Proper insulation also prevents condensation on pipes, which can also create different problems such as water droplets dripping onto floors and causing damp and mould.

Cutting off dead legs and insulating pipework is undeniably beneficial to safeguarding against Legionella, but some larger residential properties will also feature a real difference maker – a secondary hot water return system and a modern secondary hot water circulation pump.

Secondary support

Secondary hot water systems are often found in larger domestic properties and commercial buildings, providing instant hot water and recirculating it around the system in a constant loop so that it does not cool down. They are great for minimising water wastage and energy consumption. At the same time, they’re also good for preventing Legionella growth – but only if the hot water is circulating correctly and at a temperature between 50°C and 60°C.

If a property already has a secondary hot water system in place, there’s a good chance that it will incorporate a bronze pump, especially if it’s an older building. Now, these have done what has been asked of them for many, many years, though it can be argued that they are now antiquated in terms of their technology.

Traditionally made of bronze (yes, really), these pumps are often characterised by their simple three fixed speed operation, meaning they run at a constant speed and have no additional options related to setup or energy efficiency capabilities. When running at the ‘three speed’ setting, outdated bronze pumps can draw circa 100 watts.

Preventing Legionella is undeniably crucial, but it can now be done in a more efficient and functional manner. For these reasons, Wilo is making a stand and is dropping its SB30 bronze pump from August 2025 in our movement ‘The End of the Bronze Age’. In place of it, installers can choose from our popular stainless steel adjustable pumps instead, including the new Yonos PICO-Z hot water pump.

Stainless steel adjustable speed pumps are rapidly becoming the more popular choice among the plumbing and heating industry for preventing Legionella. Though they are commonly found in environments such as hospitals and schools, they now cater to the domestic market and are available in the small sizes required for such applications.

Efficient and easy to use

The next generation of hot water circulation pumps now come with many more selectable control options and, thanks to their EC motors, offer a host of efficiency benefits. The pumps’ speed (flow rate) and pressure (head) can be fine-tuned to accurately meet the demands of the system it is being used in, such as a secondary hot water return system.

The brand new Wilo Yonos PICO-Z range offers 42 flow rate settings, with an LED display to show the exact rate chosen. It also has a constant pressure (or head) setting which again offers 42 increments to ensure the required pressure is maintained within a balanced system. This added adjustability allows it to operate from as little as four watts of power to a maximum of 40 watts, and energy consumption to operate hot water systems can be reduced by up to 70% when compared to traditional bronze pumps.

On top of this, stainless steel pumps are light and easy to handle and incorporate automatic or manual venting and automatic de-blocking, both of which are functions unique to Wilo for its Yonos PICO range in heating and hot water. If any issues arise in the hot water system, this will be flagged as an error code on the pump’s LED display system, making troubleshooting a straightforward task.

Safeguarding with stainless steel

To prevent the spread of Legionella bacteria, removing dead legs and insulating pipes is crucial. Upgrading to a modern stainless steel secondary hot water circulation pump, however, can make it the perfect hat trick. Wilo’s Yonos PICO-Z range offers advanced efficiency and control options, all while offering peace of mind against the threat of Legionnaires’ disease.

Discover more about the Yonos PICO-Z range.