How long can a rental property stand empty before legionella is a risk?

There is no safe number of days. In water between 20 °C and 45 °C the bacteria multiply, and standing water drifts into that range in summer, in a warm cupboard, or in a cylinder turned down. HSE’s rule of thumb is that every outlet should be used at least once a week.

Do I have to flush an empty property every week?

That is the general principle HSE gives. Run every tap hot until it runs hot and cold until it runs cold, flush the toilets and run the showers with the spray kept down. Two minutes an outlet, and a note of the date.

Should I turn the hot water off while the property is empty?

Either keep it at 60 °C and flush weekly, or drain the system down and refill, heat and flush it before the next tenancy. What not to do is turn the cylinder down and leave lukewarm water sitting in it.

What do I do before a new tenant moves in?

Flush every outlet, check the hot water reaches temperature at the tap, clean and descale the shower heads, look at the tank lid if there is a tank, and write it down. A change of occupants is also a reason to look at the assessment again.

Do I need a new legionella risk assessment after a void?

Not automatically. If the system is unchanged and you flushed it through, confirm the assessment and date the review. If the property stood empty for a long time, if anything about the system changed, or if the new household includes someone more susceptible, reassess.

Can my letting agent do the flushing?

Yes, if your agreement says so; their inspector is often the person with the key. Whoever does it, the scheme of control should name them and the dates should be recorded.

For landlords and agents

Legionella in an empty rental property: what to do between tenancies.

Water that stands still is the risk. HSE says outlets should be used at least once a week, and that properties left vacant need careful management. Flush every outlet weekly, keep stored hot water at 60 °C or drain it, and before a new tenant moves in run the whole system through and clean the shower heads.

Why an empty house is the risky one

The bacteria want warm water that nobody moves.

Legionella multiplies in water between 20 °C and 45 °C, in water that is stored or does not move, and where there are deposits to feed on: rust, sludge, scale. An occupied house fights all three every day without trying: taps run, the cylinder cycles, the cold comes in fresh. An empty one does the opposite. The cold in the pipes warms to room temperature. The cylinder, turned down to save money, sits at 40 °C for a month. Then a new tenant arrives and has a shower.

HSE’s guidance for landlords says two things about it: “outlets on hot and cold water systems should be used at least once a week to maintain a degree of water flow and minimise the chances of stagnation”, and “there should be careful management of properties left vacant for extended periods”. Both are on the page on legionella and landlords’ responsibilities.

The weekly flush

Two minutes an outlet, once a week, written down.

Every tap, hot until it runs hot and cold until it runs cold. Kitchen, bathroom, en-suite, cloakroom, utility, outside tap.
Every shower, with the spray kept down: take the head off and run the hose into the bath or tray, or run it at low flow pointing down. The point is to move the water without filling the room with droplets.
Every toilet, flushed.
A note: the date and who did it. That note is the record that the scheme of control was followed.
Who: you, the agent’s inspector, the cleaner, a neighbour with a key. Name them in the scheme of control.

Longer voids

Keep it hot, or drain it. Never lukewarm.

For a property that will stand empty for weeks or months there are two honest choices. Keep the hot water on, stored at 60 °C, and keep flushing weekly. Or drain the system down, tank and cylinder included, and before the next tenancy refill it, bring the hot water up to temperature and flush every outlet through. The thing not to do is the thing most people do: turn the cylinder down, leave the water in it, and come back in six weeks.

Before the new tenant

Run it, heat it, clean it, look at it, write it down.

Flush every outlet as above, the day before or the day of the move.
Check the hot water reaches 50 °C at the tap within a minute, with a thermometer, and that the cold is below 20 °C within two.
Clean and descale the shower heads.
Look in the tank if there is one: lid on, water clear, insulation in place.
Look at the assessment again. A change of occupants is a reason to review it. If the system is unchanged, confirm it and date it; if the void was long or anything changed, reassess.
Give the tenant the sheet: do not turn the hot water down, clean the shower head, report hot water that is not heating properly.

Doing it

The survey asks how long it has stood empty. AI does the rest.

Do the assessment on the void, when you are in the property anyway. Your phone asks the questions, including how long the property has been empty; you take the readings and the photographs; the AI checks the survey and then produces the assessment, the tenant sheet and the written scheme of control, with the weekly flush and who does it written in. Thirty minutes to an hour, £20 a property including VAT.

Questions landlords ask

Short answers.

How long can a rental property stand empty before legionella is a risk? There is no safe number of days. In water between 20 °C and 45 °C the bacteria multiply, and standing water drifts into that range in summer, in a warm cupboard, or in a cylinder turned down. HSE’s rule of thumb is that every outlet should be used at least once a week.
Do I have to flush an empty property every week? That is the general principle HSE gives. Run every tap hot until it runs hot and cold until it runs cold, flush the toilets and run the showers with the spray kept down. Two minutes an outlet, and a note of the date.
Should I turn the hot water off while the property is empty? Either keep it at 60 °C and flush weekly, or drain the system down and refill, heat and flush it before the next tenancy. What not to do is turn the cylinder down and leave lukewarm water sitting in it.
What do I do before a new tenant moves in? Flush every outlet, check the hot water reaches temperature at the tap, clean and descale the shower heads, look at the tank lid if there is a tank, and write it down. A change of occupants is also a reason to look at the assessment again.
Do I need a new legionella risk assessment after a void? Not automatically. If the system is unchanged and you flushed it through, confirm the assessment and date the review. If the property stood empty for a long time, if anything about the system changed, or if the new household includes someone more susceptible, reassess.
Can my letting agent do the flushing? Yes, if your agreement says so; their inspector is often the person with the key. Whoever does it, the scheme of control should name them and the dates should be recorded.