Boiler Efficiency

BUFF

Perhaps we are over-complicating things because you have not previously adequately described your set up? This leads to a spiralling of the conversation which has to include potential variables as we don't know what is or isn't installed & how.
e.g. earlier you said that radiators fill with hot water from the top down, in UK domestic installations most don't as they are connected Bottom Opposite Ends.

Your 12 year old basic WB boiler almost certainly has the ability to modulate, and possibly with appropriate controls may allow advanced modulation. Potentially it is already doing that but we don't know because you havent said what they are ...

bob2302

BUFF said:

e.g. earlier you said that radiators fill with hot water from the top down, in UK domestic installations most don't as they are connected Bottom Opposite Ends.

Hot water rises on the inlet side by convection.

BUFF

yes but from the bottom where it enters under pressure ...

bob2302

BUFF said:

yes but from the bottom where it enters under pressure ...

When water goes into my radiator, at high temperature and a low average flow rate, only the first two vertical channels on the inlet side, and the top of the radiator get hot. 

My original question was about whether the efficiency of condensing boilers is significantly affected by flow temperature if the return temperature remains low. I'm guessing the answer is not much, but it wasn't really discussed.

The thread turned into a discussion about my explanation for why my return temperature is insensitive to the  flow setting. This is about the basic physics of how radiators work, so I gave no irrelevant information about my boiler.

markin

Tape a probe to the rerun pipe and tell us the results, I can tell you i cannot measure temp from feeling it i can only say its below 35c or above 45c, I can maybe guess to the closes 10c.

Underfloor heating works efficiently on  25-30c 24/7

BUFF

bob2302 said:

BUFF said:

yes but from the bottom where it enters under pressure ...

so I gave no irrelevant information about my boiler.

You didn't give much information at all about your boiler until 2/3 of the way through this post at which point we gleaned enough to say that the boiler is almost certainly capable of basic modulation. Depending upon what controller you have it may be capable of more advanced modulation.
It may well be that the boiler/controller is adjusting itself automatically to whatever changes you are making.

pensionpawn

Just as a yardstick my 19kW Viessmann, set to 20c (by Nest) for 06:30, is currently delivering an output temp of 62.4c  (set to 62c) at 28% modulation with a flue temp of 56c.