What type of pump should be used in a 300 litre unvented hot water cylinder?

Question from J Robinson, via e-mail:
Paragraph 158 of ACOP L8 advises that calorifiers (indirect unvented hot water cylinder in my case) be fitted with anti stratification pumps – to ensure water of at least 60ºC is circulated to all parts of the calorifier for a minimum of one hour per day (when the boiler is also operational) – what type of pump should be used in a 300 litre unvented hot water cylinder in a local care home?

Should it be fitted between the cold feed and DHW outlet on the cylinder, with its own time switch (set to run for one hour minimum at same time as boiler) and should there be a non-return valve below the pump on the cold water side?

Answer from Martyn Bridges, director of marketing and technical support at Worcester, Bosch Group:
I would say from your response that this is a public or commercial building, so the guidance within L8 would be a way of compliance. I think your suggestion is realistically the best way of achieving this, generally there is already a non-return valve on the mains inlet to the cylinder which would prevent the pump circulating water back down the mains, so I don’t feel you need a further valve.

It would be a requirement to fit a pump suitable for circulating potable water, typical suppliers would be Grundfos who make a brass bodied pump specifically for the circulation of domestic hot water circuits.

As for the control of the pump, I also agree with your suggestion that a separate timer designed to bring the pump on for one hour a day during the boiler programme for hot water will comply with the requirement.