Connecting a boiler to a buffer with UFH

I'd scrap the whole idea of that buffer vessel arrangement and connect directly to the UFH.
If your using standard ufh three port mixing valves then they will have the primary circulator to provide the positive pressure they need to operate properly.
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The only upside i can see to the buffer vessel is it will avoid cycling. I may be offering advice but that doesnt mean i agree with the setup.

Id also always use a primary circulator to feed the ufh, rads etc
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No I am not - I know that it is the best system available - which is presumably why you have just bought one!
OK, so you guys have sold me on the whole weather compensation thing.

If I wanted to fit one - can I?
Is it a matter of buying a controller and connecting it electrically to the boiler/stats, and off I go, or does installation require a change to the plumbing also?

Also, can anyone recommend one that would be suitable for the above setup (oil boiler, 2 tanks, one DHW one CH?)

Hi folks,just read this post and i realise its old but i am totally confused.
I am(was!!)going to hook an oil boiler up to an existing radiator circut,underfloor circut and a 300ltr dhw storage tank via buffer tank as any research i carried out seemed to suggest that connecting underfloor directly to an oil condensing boiler would be the least efficient way of doing it due to fluctuating flow rates in the underfloor circut thus causing cycling.

As i understood it the buffer would act as its name suggests and "buffer" out any flow rate implications allowing the boiler to run at maxium efficiency for the longest time possable to bring the buffer up to temp.

I had planned on adding weather comp controls to the radiator and underfloor circuts between the buffer itself and the circuts.
I planned on using a 3 port divertor valve on the dhw side to allow the dhw cylinder to be heated from the buffer or direct from the boiler as a summer/winter change over switch.

Any feedback appriciated,sorry for the loonnggg post!
The purpose of the buffer tank is to avoid burner short cycling , not so much an issue with modulating boilers utilizing high turn down ratios.

Short cycling is dependant on buffer tank volume/temp control , a correctly sized tank should be based on the max load the boiler can shift at a fixed delta T in order to avoid burner short cycling , if we were to take a 30kw boiler with a turndown ratio of 3:1 (10kw) the minimum vessel size for a 10 minute 'burner on' time would be 71 litres , this being based on hi/lo stats set at 70/50 , a 30 kw boiler with a fixed fireing rate would require a vessel size of around 215 litres for a minimum burner on time of 10 minutes. (30/84 x 600) = 214 litres)
Thought I would post here for those that have issues installing the 4xxx vaillant :LOL: , the buffer vessel would work wonders. ;)

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