Need help with install for weil mclain oil boiler
In situations like this, I generally find that the manufacturer is a more reliable source of accurate information than an installer, especially an installer whom you are not using (but then again, you might be wise not to use them, too.) Some installers learned "a particular way" which is either outdated for current equipment or was simply wrong in the first place and depend on that in exclusion to actually reading the instructions; this may not work out well. 

The manufacturer has considerably more interest in providing accurate information for successful deployment of their products.