Best Ways to Reduce Legionella Risk at Home

A solar thermal system should help your household use less energy, not create uncertainty about hot water hygiene. The best ways to reduce legionella risk come down to maintaining safe temperatures, preventing water from sitting unused, and making sure the whole stored hot-water system is checked properly rather than assumed to be working as it should.

Legionella is a naturally occurring bacterium that can multiply in certain water systems. It becomes a health concern when contaminated fine droplets are breathed in, such as from a shower. For most homeowners, sensible temperature control and regular maintenance provide effective protection without making daily life complicated.

Why legionella risk needs attention in stored hot-water systems

Legionella is most likely to grow when water remains between roughly 20°C and 45°C for extended periods. It is far less likely to survive at higher temperatures, which is why correct storage temperature is so important.

Solar thermal systems can heat water very effectively, particularly in brighter months. However, sunshine is variable, and a cylinder may not always reach a consistently high temperature throughout its full volume. A well-designed system uses its controls and supplementary heating arrangements to make sure the stored water is brought up to a safe temperature when solar gain alone is not enough.

The solar collector circuit itself is usually a separate sealed circuit containing heat-transfer fluid. The focus for legionella control is the domestic hot water stored in the cylinder and the outlets supplied by it. This distinction matters because a fault in solar performance does not automatically mean a legionella issue, but it may prevent the cylinder from reaching the temperatures it needs.

Best ways to reduce legionella risk in your home

Keep stored water at the right temperature

For a typical domestic cylinder, stored hot water should reach at least 60°C. At this temperature, legionella bacteria are controlled effectively. Water delivered at taps and showers should be limited to a safer temperature, commonly around 50°C, to reduce scalding risk.

Those two requirements can work together through correct controls and, where fitted, thermostatic mixing valves. The cylinder needs to get hot enough to protect water quality, while the water arriving at an outlet needs to be safe to use. Do not turn the stored-water temperature down simply because a tap feels too hot. That points to an outlet temperature-control issue worth investigating.

If your cylinder has a temperature display, check it occasionally rather than relying on assumptions. A reading that never reaches the expected temperature, especially through winter or during dull weather, should be assessed by a suitably experienced engineer.

Make sure a full heat-up cycle takes place

Solar thermal production changes with the weather, season and household demand. During summer, the system may provide much of your hot water. During less sunny periods, or after several cloudy days, the cylinder still needs a regular full heat-up cycle.

Many systems have controls designed to support this. The key is that the function is enabled, correctly timed and actually achieving the target temperature. An incorrectly set programmer, failed sensor, faulty valve or inaccurate thermostat can leave water warm rather than properly hot.

There is no value in guessing. A service visit can confirm how your solar thermal controls operate, whether the cylinder is achieving its target temperature, and whether any component is preventing a complete heat-up cycle.

Use every outlet regularly

Water that sits in little-used pipework can create stagnant sections where bacteria are more able to multiply. Guest bathrooms, utility sinks, outside taps, spare showers and rarely used en suites deserve particular attention.

Run both hot and cold water at seldom-used outlets at least weekly. Let each run long enough for fresh water from the main system to reach the outlet. Take care around showers and spray taps: avoid creating a fine mist close to your face while flushing, and ventilate the room where practical.

If part of a property is permanently unused, it may be better to have that section isolated or removed than to leave a redundant length of pipework connected. This is especially relevant after a renovation, layout change or conversion of a spare room.

Keep shower heads, hoses and taps clean

A shower creates the fine water droplets associated with Legionnaires' disease, so it deserves routine attention. Limescale and biofilm can build up inside shower heads and hoses, particularly in hard-water areas. Cleaning helps maintain good flow and removes the deposits that can harbour bacteria.

Remove and clean shower heads periodically in line with the manufacturer's guidance. If a hose is old, discoloured, cracked or difficult to clean, replacing it is a straightforward precaution. Taps with aerators can also collect scale, so they should not be overlooked.

Cleaning is useful, but it is not a substitute for correct stored-water temperatures. A spotless shower head connected to water that has sat too cool for too long does not solve the underlying issue.

Arrange regular servicing and fault diagnosis

A solar thermal system works through several connected parts: collectors, sensors, pumps, controls, heat exchangers, safety components and the hot-water cylinder. A problem in one area can affect the wider system's ability to heat water reliably.

Regular servicing gives an engineer the chance to check system pressure, heat-transfer fluid condition, circulation, sensor readings, control settings and cylinder temperatures. It can also identify reduced solar output before it becomes a complete loss of hot water performance.

Repair-first maintenance is often the sensible approach. A failed sensor or control setting may be a modest fix, while leaving it unresolved can affect comfort, efficiency and safe temperature management. Genuine, compatible parts and accurate diagnosis are far more valuable than replacing equipment without establishing the cause of the fault.

Situations where the risk can be higher

A household does not need to panic after a weekend away or a short holiday. Risk is generally linked to water remaining stagnant or at unsuitable temperatures for longer periods. The circumstances are different in an occupied home where water is used daily compared with a property that has been empty for weeks.

Extra care is sensible if the home has been vacant, a cylinder has been switched off, major work has altered the water system, or an old shower has not been used for months. Before normal use resumes, flush outlets carefully, check that stored water reaches its required temperature, and arrange an inspection if you are uncertain about the condition of the system.

People over 50, smokers, those with long-term lung conditions and anyone with a weakened immune system are more vulnerable to Legionnaires' disease. If someone in the household falls into a higher-risk group, consistent maintenance and prompt attention to temperature faults become even more worthwhile.

Signs that your system needs checking

Poor solar thermal performance is not always obvious. You may still have some hot water, but it may take longer to recover, run cooler than expected, or vary considerably across the week. These are reasons to investigate rather than just adjust settings repeatedly.

Look out for a cylinder temperature that stays below target, warning messages on a controller, unexplained loss of hot water, noisy circulation equipment, visible fluid leaks, or a system that has not been serviced for several years. Likewise, if your shower temperature is unpredictable, the cause should be diagnosed properly. Very hot water at one outlet and lukewarm water at another can indicate a control or distribution issue that needs professional attention.

A sensible approach for solar thermal homeowners

Good legionella control is not about constantly checking every tap. It is about having a system that heats stored water correctly, circulates it when needed, and receives proper care over its working life. Solar Thermal Guru applies that same practical approach to servicing and fault diagnosis: establish what the system is doing, explain what needs attention, and avoid unnecessary replacement work.

If you cannot confirm that your cylinder reaches a safe temperature, or your solar thermal system is no longer performing as it should, arranging a professional check is a sensible next step. A small correction now can protect both your household's comfort and the long-term condition of the system.