Hi
Just found and joined this site as the proud new (June 2011) owner of a 35 year old French property 150km north of Marseille, with a 2 year old ... yes, you guessed it, Veissmann system. Currently comprises Vitoladens 300 and Vitotronic 200 and I am in the middle of contemplating a Vitocom 100 (to be SMS ed faults) and a Vitotrol 300 - for more control, based on indoor temps.
I have spent hours fathoming this system already and am most/some(?) of the way there (possibly?!). I have TRVs but, like you, don't like/fully understand the purpose of pumping water round at 20deg (by the way your codes should mean it's never less than 20 deg). I am UK most of the time. As winter arrives, my aim, while in UK, is to heat the french house with min energy, so I am wrestling with the 1001 settings! Currently I have gone for 20hours of "setback" at default 3deg frost protection and 5 deg at not less than 35deg flow temp for a couple of hours at 7:00pmish, and 2:00amish, and I am waiting to see if this is adequate. I have the installation manuals in English with all codes etc which are probably similar to yours. I can get the pump to switch off as per the book/manuals but don't like some of the logic. eg I don't like pump noise while I'm sleeping - why do I need it running at all between 10:30pm and 7:00am, say, when I am happy to let the house cool down from 20degrees even if the outside temp hits, say -2 at 7:00pm and bottoms out at,say, -6 at say 3:00am (with day temps of around 15 deg) There are ways of keeping the pump off, which carry risk and involve faffing with codes, hence I am working on seeing if I can achieve what I want with the indoor control (Vitotrol 300) instead. My set up is in the garage under the house. Let me know if you want me to e-mail you any of these manuals.
Cheers
davro