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Two goals

you want to protect the boiler from thermal shock, most importantly. And ideally you would like nice long burner run cycles while maintaining return protection

Somewhere you will have to compromise. The heat load of the building is ever changing. If you were to adjust and install a bypass now in mild weather the dynamics will be different in full load heating conditions.

Lots of variables come into play. Is the boiler sized to the radiation? Is the radiation sized to the design load? Has the building or insulation changed since the install and calcs?

You may not gat a perfect long, efficient burn, in all load conditions regardless of the bypass, need to figure out all the variables.

The 10 minute minimun burn seems to be the number most of the respondents used when asked about cycling in the article. You should have good return temperatures in that time frame. Still think I would be more cocerned with the return temperature than the on / off cycle. Doilers will work with shorter cycles, drives me nuts, but plenty run their entire life short cycling. Low mass boilers do this commonly in low load conditions.

Sounds like you have a handle on the concept, but not quite sure how to fix it to you system. BP does a lot of these sucessfully, I'd use his method.

Here is a link to a B&G article on this subject.

http://www.bellgossett.com/press/thermalshock.htm

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