Boiler flow temperature

7 Sep 2008
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United Kingdom
I have read several articles recommending lowering the boiler temperature in the summer. The instruction booklet just tells me that the range is from 35 to 85 degrees with no guidance about winter and summer positions. My tank thermostat is set to 65 degrees so is my new boiler setting in the photo OK to deal with that? The tank is directly above on the next floor. 20220525_083219.jpg
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well if your cylinder stat shuts off then yes your boiler stat is set ok for it if not then its set too low
A problem with turning the boiler temperature down, is that you only have the one setting for both producing heating and heating up the cylinder. That boiler setting, has to produce a boiler output temperature greater than the setting of the of the hot water cylinder thermostat setting, or the boiler will cycle forever trying to heat the water in the cylinder.

Normally the cylinder stat is set for 60C, to help kill off Legionella, which means your boiler stat needs to allow your boiler to heat water ten degrees hotter, so 70C.

More modern systems allow two boiler output temperatures, one for heating, one for hot water.
My boiler has just the one control for the output temperature. I think the idea is that a high boiler water temperature isn't needed just to heat the domestic water in the cylinder. Heating off now, hopefully until October.
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a high boiler water temperature isn't needed just to heat the domestic water in the cylinder.
It is, for reasons already given above.

The concept of reducing the boiler flow temperature is for the heating, as the boiler will be more efficient at lower temperatures.
The tradeoff is that the radiators will run cooler and therefore take longer to heat the building. Whether that is a problem depends on the size of radiators relative to the room, the outside temperature and various other factors.
Summer and winter is unrelated.

Plenty of boilers are still set at 75-80 which is far too high for a modern system.

Ideally you want a boiler and controls which can have a separate flow temperature for hot water and heating.
Without those, flow should be set to the lowest setting which still heats the hot water to a suitable level, such as 60-65C, and still allows the radiators to heat the building adequately.

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