Gas boiler feeds UFH only - is a Mixer needed?

[DJKent]

Yes - that doc does say that
* https://qr.vokera.co.uk/qr?action=download&key=Generic+Document|Doc-0213599|1&name=DOCUMENTS/8a/27/8a27lp9bftbwb_xezjgbjt4mzynboc1ruclfk93dmsr._h_

The boiler is weird tho - on heat-demand it runs at a fixed 75% heat for 15 minutes - and only after 15 minutes does it adjust flame to suit the demand..... 15 minutes seems a long time?

 

[John.g]

Thats the same wording in my relations Vokera Vision 20S but that certainly modulates within seconds of firing up, I would read this to mean that it limits the boiler to 75% of its max output for 15 minutes after every fire up and then allows it to reach 100% output, if required.

 

[DJKent]

it's weird anyway - to have a 15 minute limitation on every fire up?

 

[John.g]

It does on the one hand, one might expect it to only operate if the boiler temperature is very low after a prolonged outage, but, on the other hand, full output will not be required if the boiler is cycling which will only happen if the demand is continuously below the boiler's minimum output.

The restriction doesn't apply to the DHW side of a combi.