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FM legionella check on continuous flow hot water heating units and delivery systems

21 May 2020

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.

This will necessitate that certain procedures and measures are carried out before the system can be made ‘live’ and function efficiently.

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.

Start 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 please note 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 degree C (if it is not already)
2. Open gas supply.
3. Turn on 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 had a service within the last 4/5 months, then a full service should be carried out before above steps 1 – 5 are carried out.

Other modes of hot water delivery systems will have their own sets of procedures.

Best advice to site managers and maintenance personnel is to ensure they should obtain specific sets of information and procedures for their particular system.

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.

Or sites may want to consider that it is the perfect opportunity to switch 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.

Continuous flow is acknowledged as more technologically advanced, more efficient, more cost effective with less front-end costs and better Whole of Life economics.

• Comprehensive Restart Kits are readily available direct from Rinnai. If there are any questions or queries regarding continuous flow hot water heating systems please contact Rinnai direct by telephone or email.

• FM, Installers, site managers, contractors and all end-users simply call 01928 531870, select technical and if the call is not answered immediately leave a voicemail. Response will be within one hour between 0800 – 22:30 / 7 days a week. This means that there be a technical response every day of the week.

• Email or

• Visit and see the website homepage “Help Me Choose” or “Ask Us a Question”.

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