Home / The guide / Heating and cooling

Control legionella and scalding

Legionella bacteria multiply in lukewarm water, which is a risk with solar preheat tanks that sit warm. UK HSE guidance gives clear temperature targets.

How

1. Store hot water at 60 C or above (HSE).
2. Aim for hot water reaching outlets at 50 C or above, and keep cold water below 20 C.
3. Know the danger band: HSE says legionella multiplies between 20 and 45 C.
4. Raise solar preheat tanks to 60 C regularly with the backup, or keep them small.
5. Fit thermostatic mixing valves close to outlets used by children or older people to prevent scalds.
6. Flush rarely used outlets weekly and descale showerheads quarterly.

Safety: Water at 60 C can scald in seconds. Mixing valves are essential where scalding is a risk.

Sources

1. Managing legionella in hot and cold water systems. UK Health and Safety Executive, accessed 2026-11

Open in the interactive guide