Letting triggers a duty. Selling, in most cases, does not. If you let a UK property you have a legal duty to assess and control the risk of exposure to Legionella in the water system you provide [1]. If you sell, that duty moves to the buyer at completion — you are not separately required to produce an assessment to make the sale.
That single split clears up most of the confusion behind this question, because the word “or” in the title hides two very different situations. The detail that matters is whether you are about to become, or stop being, the person in control of the water system. The questions below take the common searches one at a time.
Do I need a Legionella risk assessment to let my property?
Yes — in the sense that you must assess and control the risk and keep a record that you did [1]. There is no separate “letting test” in Legionella law; the duty is continuous for as long as you provide the water system, and the start of a tenancy is simply when it becomes most visible. For an ordinary flat or house the assessment is usually short and the risk low, because the system is small and water is used often [1]. What you are required to hold is a proportionate, dated assessment, not a glossy pass certificate.
Do I need a Legionella risk assessment to sell my property?
For a normal residential sale, no. There is no statutory requirement to commission a Legionella risk assessment in order to sell a home, and nothing in the conveyancing process that demands one the way an EPC is demanded. At completion the duty passes to the new owner or occupier, who then assesses the system they control. The pragmatic exception is commercial or mixed-use property, where a buyer’s solicitor may ask for an existing assessment as part of due diligence — more on that below.
Is a “Legionella certificate” the same as a risk assessment?
No, and the difference is worth getting straight before you pay for anything. There is no statutory “Legionella certificate” for residential lettings [1]. A risk assessment is a record of judgement: someone looked at the system, decided how much risk it carries, and noted any actions and a review date. A certificate sold as a flat-fee product before each let proves little on its own. Buy competence and a real assessment if you want them. Do not buy a certificate because a firm implied the law requires the word.
Who is responsible once the property is sold or let?
Control follows occupation. The duty sits with the person in control of the premises, and appointing an agent to do the day-to-day work does not move the accountability off you [2]. When you sell, control transfers to the buyer and the Legionella duty goes with it. When you let, you keep the duty for the system you provide as landlord, while the tenant carries the everyday job of using the water — running taps, cleaning the shower head — that keeps risk down. The split is cleanest when it is written down in the tenancy paperwork rather than assumed.
What does the record actually need to show?
Enough to prove you assessed the system and acted proportionately. For a simple home that can be a single page: where water is stored, how hot the hot water runs and how cold the cold stays, whether any outlets sit unused, the conclusion (commonly “risk low”), any actions, and a review date [1]. The exact temperatures and intervals you cite should come from your own assessment rather than a rule of thumb — let the site-specific judgement set the figure. A defensible record is short, dated, and honest about what you checked.
Does selling a commercial property change the answer?
Often, yes. On a commercial or mixed-use sale, the systems are usually larger and the buyer’s advisers more thorough, so an existing Legionella risk assessment frequently appears on the due-diligence list alongside asbestos and fire records. You are still not legally compelled to create one purely to sell. But a current, credible assessment can smooth the transaction and avoid a retention or a renegotiation, because it shows the incoming duty holder what they are taking on. In my view, for any property with a calorifier, a cold-water storage tank, or long pipe runs, having the assessment ready is simply good selling, never mind compliance.
How often does the assessment need redoing once I am letting?
Review it when something changes, and otherwise at the interval your own assessment set [3]. New plant or pipework, a long void between tenancies, a more vulnerable occupant, or an alteration like a loft-conversion bathroom are all triggers to reopen it. The review can be quick when nothing material has changed — the point is that it happened and you can show it. An assessment dated years ago and never reopened, despite a new boiler and three tenancies since, is the pattern that gets landlords caught out.
What should I do before a new tenant moves in?
Flush the system through. The void between tenancies is where a low-risk home briefly becomes a real one: taps and showers sit untouched, warm still water builds up in the pipework and the shower head, and then the new tenant runs that shower on day one. Run the taps and shower long enough for the water to turn over before re-letting, and do the same after any extended empty period. Legionella control in residential rental properties covers the underlying controls — temperature and turnover — in more depth.
Where this guidance stops
This is general guidance for the point of letting or selling, not legal advice, and it does not replace assessing the actual property. Some lets sit outside the “small and simple” picture: a house in multiple occupation, a tank in a warm loft, a tenant who is elderly or immunosuppressed, or any larger system can shift the risk and may justify a competent assessor. Where a sale involves commercial plant, treat the assessment as part of the deal rather than an afterthought. If you are unsure which side of the let/sell line your duty falls on, that uncertainty is itself a reason to get a competent opinion before you sign anything.
If you only do one thing today, do this: for a property you are letting, complete a dated, proportionate risk assessment and pair it with a record of flushing the system before the tenancy starts. Keep the two together. Moving those records off a loose spreadsheet and into a digital logbook makes the review dates, flush logs, and assessment all retrievable in one place when a tenant, an agent, or an inspector asks — which is exactly when paper tends to be missing. For the wider landlord picture, Landlord responsibilities for Legionella in rental properties is the next read.
Sources
[1] HSE, “Legionella and landlords’ responsibilities”. https://www.hse.gov.uk/legionnaires/legionella-landlords-responsibilities.htm [2] HSE, “Legionnaires’ disease - what you must do”. https://www.hse.gov.uk/legionnaires/what-you-must-do/index.htm [3] HSE, “Legionnaires’ disease. The control of legionella bacteria in water systems - ACoP and guidance (L8)”. https://www.hse.gov.uk/pubns/books/l8.htm