Running a boiler at the minimum temperature that will adequately heat the property will extract more heat energy from the combustion products (obviously it is easier with weather compensation since the set temperature is automatically matched).
However, the increased condensation occurring within the boiler heat exchanger may result in a reduced boiler life due to increased corrosion...more so without adequate servicing.
I suspect many manufacturers are being very cautious especially when they offer extended warranties. There is considerable incompetence within manufacturer design teams....producing products with many design faults, often only coming to light several years after the initial product launch, hence marketing departments may say one thing......"run at maximum temperature" despite the common knowledge to run as low as possible.
Another gem from their literature....."The heat cell can be cleaned in situ via an inspection hatch saving time during service." Their boilers with this particular heat exchanger take a couple of hours to thoroughly service....right PITA. And when the boiler is right flued the inspection hatch is under the flue
Are Worcester not introducing weather compensation on some of their range? I suppose the increased corrosion within the heat exchanger will be balanced out by the reduction in the plastic junk bottom end not going brittle and the O rings cooking
The 11C drop was originally derived from the old Farenheit 180-160 design criteria....heat exchangers were inefficient and raising the temperature by 20F was felt appropriate. This gave an average radiator temperature of around 76C and radiators were sized accordingly. High efficiency heat exchangers can raise the temperature by 20C (provided the manufacturer quotes this in their literature) but allowing a 20C drop lowers the average radiator temperature and on a sufficiently cold day they may not heat the room to the required temperature. There are advantages though eg the increased drop doubles the heat capacity of the pipework allowing reduced installation cost (albeit the rads need to be a little oversized). Manufacturers have to cope with old systems with the traditional 11C drop and newer systems perhaps designed on a 20C drop...hence the ambiguity.
Having designed a particular system with oversized rads to allow maximum flow temperatures of just 55-60C (even when snowing outside) I can tell you the heat exchanger was in a real state after the first year. It actually appeared to have snowed inside given the significant oxide buildup....it will be interesting to see its appearance at this years service visit.
