uRisk quickly carried out a full legionella risk assessment and sampling plan to determine the high risk areas that encouraged the growth. The breeding area was identified as a TMV installed on the flow immediately downstream of the hot water cylinder. This meant that whilst the hot water cylinder was set to 60-65°C to reduce the risk from legionella growth, the TMV reduced the hot water pipework immediately to 41°C, to then distribute at this temperature around the entire hot water system. This created Legionella positive results of 3,500 CFU/mL.
As per the HSG 274 Part 2 legionella guidelines for hot and cold systems, TMVs should be installed within 2m of each water outlet (tap) to keep the hot water distribution above 50°C (55°C in healthcare). In this case, the only TMV present was well over the 2m from each outlet as it was situated on the cylinder. The TMV needed to be removed from the cylinder flow so that hot water could distributed around the hot water pipework at 55-60°C. With the hot water only being reduced to 41°C locally under each outlet. This would help to discourage legionella from growing, whilst also protecting users from scalding temperatures.