What temperature should hot water be stored at?
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Key points
- Store hot water at at least 60°C in the cylinder or calorifier — this is the figure that suppresses legionella in the vessel where water sits.
- Hot water should reach at least 50°C at the outlet within one minute of running, and 55°C in healthcare premises.
- The two numbers are a chain, not a choice: store at 60°C so the farthest tap still arrives above 50°C after heat losses in the pipework.
- Cylinders stratify — the base is always cooler than the thermostat shows — which is why setting storage below 60°C leaves a growth zone exactly where sediment collects.
- Hotter storage raises a scalding risk that is managed at the outlet with thermostatic mixing valves, not by turning the cylinder down.
Hot water should be stored at at least 60°C. That is the figure in HSG274 for cylinders and calorifiers, chosen because legionella cannot survive sustained temperatures at that level, and water sits in a storage vessel for hours at a time. The stored water is then distributed so that it reaches every outlet at at least 50°C within one minute of running — 55°C in healthcare premises, where the occupants are more vulnerable.
Why 60°C storage and 50°C at the tap are one rule, not two
People often quote one number or the other, but the system only works as a chain. Water cools as it travels: through the flow pipe from the cylinder, around the distribution loop, and down the branch to the tap. If you store at exactly 50°C, the water arriving at a distant bathroom is already in the legionella growth range of 20°C to 45°C by the time it gets there. Storing at 60°C builds in the headroom that lets every point in the system stay above 50°C despite those losses. The return leg of a circulating system matters too: water coming back to the calorifier should still be at 50°C or above, which is the check that the loop is not bleeding heat somewhere. Our temperature chart sets out all the figures together, and legionella temperature control explains how the monitoring fits around them.
The stratification problem: why 55°C on the thermostat is not 55°C in the tank
A hot water cylinder does not hold one uniform temperature. Hot water rises, so the top of the vessel — where the thermostat usually sits — is the hottest point, and the base, where cold feed water enters and sediment settles, is always cooler. A cylinder set to 55°C can easily hold water at 40°C at the base: squarely in the growth range, in exactly the layer where debris and biofilm accumulate. This is why the guidance figure is a minimum of 60°C rather than a target of 50-something, and why a calorifier inspection includes checking the temperature at the base and drawing a sample from the drain valve, not just reading the thermostat.
Free legionella risk assessment template
A structured Word document following the five-step approach in ACOP L8. Covers risk identification, written scheme, monitoring, and records. If it isn't written down, you can't evidence it.
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The scalding objection, and why it does not change the number
The most common reason cylinders get turned down is scalding, and the concern is legitimate: water at 60°C can scald in seconds. But the answer the guidance gives is not to cool the store — it is to control the temperature at the point of use. A thermostatic mixing valve blends the stored hot water with cold to deliver a safe temperature at the tap while the system behind it stays hot enough to suppress legionella. The two duties are reconciled by engineering, not by compromise, and our page on balancing scalding risk against legionella works through exactly how. Turning the cylinder down to 45°C solves the scald risk by creating a legionella risk, which is no solution at all.
Store at 60°C, deliver at 50°C, and manage the scald risk at the tap with a mixing valve. Cooling the cylinder to prevent scalds trades one controlled risk for one you cannot see.
Checking and recording the figures
The storage temperature is one of the routine monitoring points in any written scheme of control: calorifier flow and return temperatures monthly, and hot water at sentinel outlets — the nearest and farthest from the heat source — monthly as well. Each check should be recorded with the date, the outlet, and the reading, in a log book kept for at least five years. A cylinder that will not hold 60°C, or a loop whose return comes back cool, is a fault to investigate rather than a number to note and forget, and repeated failures belong in front of whoever services the system. The temperature checker structures exactly this record.
Free legionella risk assessment template
A structured Word document following the five-step approach in ACOP L8. Covers risk identification, written scheme, monitoring, and records. If it isn't written down, you can't evidence it.
Follows ACoP L8 and HSG274 Part 2. Free. No spam.
Frequently asked questions
What temperature should a hot water cylinder be set at?
Store hot water at at least 60°C in the cylinder or calorifier. Storage at 60°C keeps the whole body of stored water above the temperature at which legionella dies, while the distribution system then delivers it to outlets at at least 50°C within one minute of running. Setting the cylinder thermostat below 60°C saves a little energy but lets the cooler water at the base of the tank sit in the legionella growth range.
Why is hot water stored at 60°C but used at 50°C?
The two numbers do different jobs. The 60°C storage figure is about killing and suppressing legionella in the vessel where water sits for hours; the 50°C outlet figure (55°C in healthcare) is about keeping every point of the distribution pipework above the growth range while accepting that water loses heat on its way to the tap. Storing at 60°C gives the system enough headroom that even the farthest outlet still arrives above 50°C.
Is 55°C hot enough for a hot water cylinder?
No, not as a storage temperature. Legionella begins to die at around 50°C and dies increasingly quickly above that, but the guidance figure for stored hot water is at least 60°C, because a cylinder stratifies: the water at the base is always cooler than the thermostat reading at the top. A cylinder set to 55°C can have a base temperature well inside the growth range, which is exactly where sediment and legionella accumulate.
Does a combi boiler need to be set to 60°C?
A combi boiler heats water on demand and stores nothing, so there is no stored body of water for legionella to grow in, and the 60°C storage figure does not apply in the same way. The hot water outlet temperature still needs to reach at least 50°C within a minute at the tap, and the rest of the system — any tanks, long pipe runs and little-used outlets — still needs the usual attention. The legionella risk in a combi system is lower, not zero.
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