Setting of boiler temperature

[sargan]

Looking to set up my boiler for maximum efficiency

System from boiler perspective is very simple .. Baxi Barcelona connected to a Thermal Store (EnergyMaster) - whole contents of store pump circulated around boiler ... no rads.
Store thermostat is what decides whether there is a call for heat from the boiler ... stat, is on lower 1/3 rd and set at 65 degrees (can't be set any higher due underfloor heating system requirements.

My question is on the temperature setting on the boiler, originally boiler had been set to Max ... this was on advice of Underfloor heating system supplier, though when I questioned them this week ... they advise needs to be set for best efficiency ..when I questioned what that was , they said by monitoring performance and pad consumption (not very helpful) .. but must always be set higher than setting of tank stat.

Be interested in what is the best method of figuring out the boiler setting, need to make sure it stays in condensing mode & is as efficient as possible.

Should I just adjust boiler to highest setting that obtains a return temp of lower than 65 degrees .... but when, at initial request for burn or towards end of burn cycle ?

 

[Stoney Ground]

Boiler will not condense unless return temperature is below 55°C.

 

[Darren Jackson]

" stat, is on lower 1/3 rd and set at 65 degrees (can't be set any higher due underfloor heating system requirements". UFH blending valve will ensure correct temperature for the floor heating so turning up the boiler should not affect it.

 

[sargan]

There is no blending valve on UFH loop only on DHW. That is why store stat is set to 65

There are 2 heat exchangers .. upper for DHW lower for UFH ... and there is a baffle across store to control stratification.
I do plan to add a mixer valve on UFH ... but it is not in the design installed (package desiged & supplied by NuHeat)

 

[sargan]

There is no blending valve on UFH loop only on DHW. That is why store stat is set to 65

There are 2 heat exchangers .. upper for DHW lower for UFH ... and there is a baffle across store to control stratification.
I do plan to add a mixer valve on UFH ... but it is not in the design installed (package designed & supplied by NuHeat)

Here is a basic sketch if that helps ... (bypass & pressure vessels omitted for clarity)

 

[sargan]

Here is a basic sketch if that helps ... (bypass & pressure vessels omitted for clarity)

View attachment 27996

NuHeat state 2 conditions:
# The boiler thermostat is set to achieve a water temp should be set to 75C

# The temperature difference between flow and return pipes does not exceed 13 C

So I'm confused here - the comment above (STONEYGROUND) advises return temp must be 55 to be condensing ........ how can I get to that from a 75C flow ...... that would be 20C differential and therefore greater than 13 C