Legionella in Empty Properties: Voids, Holiday Homes and Reopening

Empty properties grow Legionella, because water sits warm and stagnant. Any property left vacant for more than a week needs a flushing regime. After longer vacancies you also need a reopening procedure — flush, verify temperatures, check showerheads and tanks, and consider disinfection. The risk is real but the controls are simple.

Why empty properties are high-risk

Two things happen when a building stops being used:

• Stagnation. Water in pipework, calorifiers, cylinders and tanks stops moving. Even with heating off, cold pipework in a heated structure can sit warm; hot cylinders that switch off cool through the danger zone. With nothing being drawn, none of it gets renewed.
• Aerosol on return. The first person back turns on a shower or a spray tap and inhales the resulting aerosol, which has been brewing for weeks. This is the textbook Legionnaires' exposure scenario.

The flushing regime — weekly, at minimum

For any property left vacant — a void, a holiday home, a second home, an office between tenants — the routine should be at least weekly:

1. 1

   Run every cold outlet

   For 2 minutes, or until the water has cleared and the temperature is below 20°C.

2. 2

   Run every hot outlet

   For 2 minutes, or until it reaches at least 50°C within 1 minute.

3. 3

   Manage shower aerosols

   Either remove the head and run the hose into the tray, or bag the head and run to minimise aerosol. Don't stand over a closed shower cubicle running a stagnant shower at full flow.

4. 4

   Cycle through TMVs / mixers

   Run on full hot, then full cold, then blended — so the full range of internal passages is flushed.

5. 5

   Record

   Date, who did it, anything noted. A simple log is fine — but is the evidence the regime actually happened.

Longer vacancies — what changes

A safe reopening procedure

The HSE's reopening guidance issued during the COVID closures is still the cleanest template for a property that's been shut for an extended period. The shape of it:

1. 1

   Review and update the risk assessment

   Acknowledge the period of disuse; identify which controls lapsed; plan the recommissioning.

2. 2

   Inspect the cold water tank

   Lid, screens, water condition, temperature. Clean if conditions warrant — see our cold water tank cleaning guide.

3. 3

   Bring the hot system up properly

   Recover storage to 60°C and circulate. Don't just give it a few hours and call it done — verify temperatures at sentinels.

4. 4

   Whole-system flush

   Outlet by outlet, hot and cold, in a logical order (furthest first). Manage aerosols at showers.

5. 5

   Clean / replace showerheads and aerator fittings

   Descaling or replacement of heads that have sat unused. Aerators are an aerosol-generating risk if dirty.

6. 6

   Service / verify TMVs

   Test blended temperatures and fail-safe shutoff before returning to use.

7. 7

   Sample where appropriate

   For vulnerable users or higher-risk premises, take Legionella samples and stand the system down until results are known if the risk justifies it.

8. 8

   Record everything

   What you did, when, by whom, with results. The documentary trail is part of the duty.

Practical tips for the real world

• Schedule flushing as a calendar task. "Every Friday morning" is more likely to actually happen than "weekly".
• Run the kitchen tap first, then bathroom basin, then shower — least to most aerosol risk.
• Don't power down the cylinder to "save money" while vacant. A cylinder cycling on the safety set point is fine; a cold cylinder gathering Legionella is not.
• Empty insulated lofts in winter can freeze tanks; in summer they can roast them. Both are problems — fix the location, not just the cleaning frequency.
• Document the flushing — even a clipboard in the airing cupboard with dates and initials is evidence that the regime exists.

Frequently Asked Questions

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