Lower Boiler Temperature To Save Energy

[Deleted User]

Have a read of this blog written by a qualified heating engineer.

https://theintergasshop.co.uk/content/195-to-reduce-flow-temperature-or-not-reduce-flow-temperature-is-that-the-question

As far as Legionella is concerned, this is the advice from the industry. The risk increases markedly if the water is stored for a long period at low temperatures. (How many people heat their HW cylinder up to 70C when returning from holiday before using it: I suspect not that many.)

Here’s a quick summary of the effect of temperature in degrees Celsius on Legionella:

20° or less – Legionella survives, but in a dormant state

20° to 45° – Legionella will grow rapidly

50° – Most Legionella bacteria will die within hours

60° – Most Legionella will die within minutes

70° – All Legionella bacteria will die instantly

FWiW, I choose to run my system boiler at a low temperature AND I re-heat my HW cylinder via the immersion heater. The maths work for me as I am on an EV tariff with a low offpeak charge. The limiting factor on a system boiler is that the boiler flow temperature cannot be set below the HW maximum temperature: in such circumstances, the cylinder would never reach maximum temperature.