On 03/11/2020 19:08:29, Harry Bloomfield wrote:
Tim Lamb used his keyboard to write :

I was a bit taken by surprise when someone recently suggested that
condensing boilers work best at 65 deg. C.* My thought was that it
does not leave much room for DHW at 60deg. to avoid bacteria.

Modern boiler have separate temperatures for CH to HW. 65C is the
maximum for efficient condensing, ideally it needs to be less than that
- I have mine set for Max 60C for CH, Max 80C for HW production.

I thought efficiency was determined by return temperature, and not flow
side temperature?