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Legionella Checks on Water Heating Systems Essential, says Rinnai

Legionella Checks On Water Heating Systems Essential, Says Rinnai
23 June 2020 | Updated 24 June 2020

As buildings are reoccupied, Rinnai is recommending a series of procedures on continuous flow hot water systems before bringing them into active service.

All hot water delivery systems in any commercial or institutional site need to be given detailed consideration to the potential of Legionella proliferation during the shutdown, says Rinnai.


HSE Guidelines


ACOP L8 guidelines, produced and published by the Health & Safety Executive, lists the details and necessary procedures to ensure system cleanliness. According to ACOP L8, continuous flow direct to outlet systems are seen as low risk for Legionella, due to it allowing for a full turn-over of water volume, no stored water and accurate temperature control.

However, stagnant water can pose a risk to users of a building, so it is essential that any water system is prepared and refreshed after a building has been left unused.

N Series 5 Hot Water System

Picture: A diagram showing a hot water system


Inspection Tips


Rinnai advises starting with an inspection. The first and most important point of a comprehensive and detailed inspection of the appliances is to ensure they can operate to maximum efficiency, especially if there is no record of what procedures were taken when the system was shut down.

So, to bring a continuous flow hot water heating system back to into active service, Rinnai notes the following procedures and consideration:


  • With the water heaters still shut down, allow fresh cold water into the system and flush all outlets for a minimum of 5 minutes. This will allow all stagnant water to be removed which should take any bacteria with it. Another method can be to flush the system with a suitable biocide chemical
  • Once the above has occurred and, if the appliance has followed a regular and appropriate service regime, the water heater can be brought into service and the below steps carried out:


  1. Set appliance to 65 degrees C (if it is not already)
  2. Open gas supply
  3. Turn on the secondary pump, check water heater is operating correctly by checking gas pressures and allow to recirculate for no less than 1 hour
  4. After one hour if possible, adjust TMS’v to 55 degrees and flush all outlets for a minimum of 5 minutes
  5. Carry out sample tests for all water outlets for any Legionella presence
  6. If the appliance has not been serviced within the last 4/5 months, then a full service should be carried out before above steps 1 – 5 are carried out


Lockdown Has Been An Ideal Time For Bacteria Proliferation


Other modes of hot water delivery systems will have their own sets of procedures. Rinnai’s advice to site managers and maintenance personnel is to ensure specific sets of information for their particular system is obtained. 

This may be time-consuming, but it is important to check for possible Legionella given that the lockdown has been here for several weeks – and it has been an ideal time for bacteria proliferation.

Sites may also want to consider switching to a continuous flow system of hot water delivery. This will ensure a limitless supply of hot water is available, provided there is no interruption to gas and water supplies.

Picture: A graphic showing Legionella bacteria. Image credit: Water Treatment Services Ltd

Article written by Ella Tansley | Published 23 June 2020


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