What happens if you set a flow temperature lower than HW cylinder

[HRP123]

Hi there, I was wondering if you set a boiler flow temperature at lets say 50 degrees and your unvented indirect cylinder is at 55 degrees - is it the case your cylinder will never reach up to temperature, or will it reach the temperature but just take longer? I have an older boiler where I can set only one flow temperature with a LLH - and although the UFH and rads would be OK with a lower temp - I'm wondering how it affects the HW cylinder. I am aware that it is worth running the HW at 60 once in a while to kill off bacteria.

 

[ShaunCorbs]

Correct cylinder will never satisfy also higher chances of legionnaires the lower you go

 

[gmartine]

We're naturally getting alot of this type of enquiry about lowering boiler flow temp but still managing to keep the HW storage in a safe manner but usually with less than capable boiler.

I'm not sure it could apply to the OP with his huge HW storage requirements but as you only need a legionella cycle once a week as an easy work around why not do it electrically? As long as you have an immersion in the lower half of the cylinder to heat all the cylinder water set it via a timer to come on overnight for an hour or three to raise the store temp to 60/65 deg. The rest of the time the HW cylinder temp can be set to the boiler flow temp which will be ample especially for unvented with decent flow rate and pressure.

 

[HRP123]

We're naturally getting alot of this type of enquiry about lowering boiler flow temp but still managing to keep the HW storage in a safe manner but usually with less than capable boiler.

I'm not sure it could apply to the OP with his huge HW storage requirements but as you only need a legionella cycle once a week as an easy work around why not do it electrically? As long as you have an immersion in the lower half of the cylinder to heat all the cylinder water set it via a timer to come on overnight for an hour or three to raise the store temp to 60/65 deg. The rest of the time the HW cylinder temp can be set to the boiler flow temp which will be ample especially for unvented with decent flow rate and pressure.

Sorry I missed this message. I have in fact installed an Eddi (solar / timer boost) which I am planning to use for setting up the 60 degree boost on the weekend using off peak energy. Thanks