legionella temperature check failed what to do

Direct answer. When a hot or cold water temperature reading falls outside the building's legionella control scheme, do not mark the check complete and wait for the next scheduled round. Confirm the measurement and outlet, alert the responsible person, assess whether people are exposed to an uncontrolled system, investigate why the temperature is wrong, apply proportionate interim controls, repair the cause and verify that the system has returned to its intended regime. Record the original result, decisions, action and repeat evidence. The right response depends on the actual system, building users and written control scheme; a single low reading does not automatically prove legionella contamination, and a later normal reading does not by itself prove the underlying defect has been fixed. HSE hot and cold water systems; HSE L8.

This is an England facilities response guide, distinct from the existing legionella risk-assessment explainer, which owns the general duty and control-scheme question. The legionella compliance software page is the commercial owner. This article neither diagnoses a water system remotely nor claims a Complys temperature sensor, alarm or laboratory-testing capability.

Know the control target for the specific system

HSE explains that temperature control is a traditional strategy for hot and cold water systems. Its general guidance says cold water should, where possible, remain below 20°C, hot water should be stored at at least 60°C, and distributed hot water should reach 50°C within one minute at outlets; HSE cites 55°C in healthcare premises. Those values are not a one-size-fits-all instruction to alter a thermostat or remove anti-scald protection. A competent person must interpret the system design, mixing valves, vulnerable users and the site's written scheme. HSE hot and cold water systems.

Check what was actually measured: storage temperature, return temperature, sentinel outlet, representative outlet, a mixed outlet or a surface probe. A mixed tap downstream of a thermostatic mixing valve (TMV) should not be evaluated as if it were an unmixed hot-water distribution point. A cold tap that has warmed because its pipe runs beside a hot main tells a different story from a tank whose whole supply is warm. Record the outlet and method so the responsible person can distinguish a local issue from a system failure.

Example. A facilities operative notes 44°C at an unmixed hot sentinel outlet after one minute, while the calorifier shows 61°C. The temperature target at the storage vessel may be met, but the outlet result could indicate a local circulation, balancing or long-leg problem. The operative should follow the site's escalation scheme and seek a competent investigation; turning the calorifier higher without understanding the system may raise scald risk and miss the circulation fault.

Confirm the reading safely

Before escalating a faulty instrument reading as a system fault, check the thermometer's identity, calibration or verification status, measurement method, elapsed time and outlet label. Repeat the measurement as the written scheme directs, without treating repeat testing as permission to ignore an initial abnormal value. Note if the outlet has been unused or if a mixing valve or outlet attachment affects the result. For hot water, avoid exposing people to scalding temperatures during the check.

Do not delete the first reading after obtaining a normal one. Keep both, with times and method. An intermittent failure can be operationally important: a recirculation pump may stop periodically, or temperature may fall at peak demand. Where the person collecting readings lacks technical competence to interpret them, their responsibility is to report accurately and escalate, not to diagnose from one number.

The HSE recommends that monitoring be based on the risk assessment and that records identify who did the work and when. Remote sensing may help detect control-regime failure but should be implemented on a specific assessment and competent advice; an automatic reading is still only evidence to be interpreted. HSE keeping records.

Assess risk and decide interim controls

The responsible person should determine which outlets and users may be affected, how long the condition may have existed and whether alternative controls remain effective. Consider showers or other aerosol-producing outlets, vulnerable users, high-use areas, dead legs, stagnation, recent maintenance and whether the fault is isolated or widespread. HSE's risk-assessment guidance specifically considers water at 20–45°C, storage and recirculation, nutrients and the creation of aerosols. HSE identifying and assessing sources of risk.

Interim measures may include restricting an outlet, providing an alternative supply, increasing appropriate flushing, arranging further monitoring or seeking specialist water-hygiene advice. The correct choice is system-specific; simply flushing a defective system can create aerosols if done badly and may not correct a failed control. If healthcare or other vulnerable populations are involved, use the relevant specialist protocol and involve the responsible clinical or infection-prevention team as appropriate. Do not derive a universal closure period from this page.

Record why an outlet remained open or was restricted, who authorised the decision, when it will be reviewed and what evidence will release the restriction. A visible “out of use” sign is useful only if it prevents the actual exposure pathway and is communicated to cleaners, residents, staff and contractors who may otherwise turn the outlet back on.

Find and fix the cause

Work from the system schematic and control scheme. Possible causes include failed hot-water circulation, poor balancing, a heater or thermostat defect, excessive draw-off, heat gain in cold-water pipework, inadequate insulation, a stuck valve, a long leg, stagnation or an altered mixing arrangement. These are investigation prompts, not a diagnosis for a particular site. HSE's HSG274 Part 2 gives detailed monitoring and technical guidance for hot and cold water systems; use a competent person to determine the repair and any disinfection or sampling needs. HSG274 Part 2.

Ask whether recent building work, occupancy change or shutdown altered the system. A new outlet can create a long branch. A vacant wing may leave water unused. A valve closed during maintenance may prevent circulation. The failure may reveal that the schematic or monitoring point list is outdated, so update those records as part of the corrective action.

Do not assume chemical treatment, thermal disinfection or laboratory sampling is automatically the first remedy. HSE says the risk assessment and written scheme should determine cleaning, disinfection and other controls. Sampling, where used, should have a defined purpose and competent laboratory method. A negative sample cannot excuse a known failed control regime. HSE preventing or controlling risk; HSE testing and monitoring.

Verify the whole control chain

After a repair, verify the relevant readings at the affected point and representative related points, as advised by the competent person. If a circulation fault was suspected, a single outlet reading immediately after manual flushing may not prove the return loop works throughout normal operation. If a cold-water line was warmed by neighbouring pipework, test under realistic demand and ambient conditions. If a TMV or outlet was changed, check both legionella control and scald protection.

Close the action only when the system operates within the intended scheme, defects have been remedied, interim restrictions can be removed and responsible people have been told. Keep repair reports and follow-up readings together. Set a short review if the failure was intermittent. Revise the written scheme or risk assessment if the original monitoring frequency, sentinel points or escalation rule failed to detect a meaningful loss of control. HSE keeping records.

The record should make a future audit straightforward: what failed, who was exposed, what was done, what demonstrated restored control, and who authorised closure? A spreadsheet cell changed from red to green without those answers is weak evidence.

Common mistakes

• Comparing a TMV mixed outlet with an unmixed hot-water distribution target.
• Deleting or overwriting the first abnormal reading after a normal repeat.
• Turning up a heater without investigating circulation, scalding and system design.
• Assuming an out-of-range reading equals a positive legionella sample, or that a negative sample proves a faulty control is acceptable.
• Leaving an affected shower in use while ownership of the decision is unclear.
• Closing the action when work is ordered, before repair and verification.
• Correcting one outlet without checking related points and the written scheme.

Where Complys fits

The legionella compliance software page is the right commercial owner for evaluating how a facilities team organises water-hygiene records and actions. This article does not claim Complys measures water temperature, connects to sensors, analyses samples, prescribes treatment or certifies system safety. The practical next step is to take one recent failed reading and verify that its escalation, interim decision, cause, repair and follow-up readings form a complete evidence trail.

Primary sources checked 4 October 2026

• HSE hot and cold water systems — general temperature strategy and different premises.
• HSE L8 and HSG274 Part 2 — control framework and technical guidance.
• HSE risk assessment, control and records.

Publication gate: A competent water-hygiene reviewer should check any later building-specific target, corrective action or sampling instruction. Recheck HSE guidance and the relevant site's written scheme before publication.