This article includes detailed information on the Flo Smart Water Monitor and Shutoff, also known as the Flo by Moen Water Shutoff.
Hydronic boilers operate in the pressure range between 10 and 30 psi. Water feed to the piping network goes through a separate pressure reducing valve (boiler feed regulator) that regulates below system static pressure. 12 psi is a standard setting for the boiler feeds. If the boiler loses water due to small leaks/evaporation the boiler feed will open to supply make-up water. Unless the equipment has been drained for servicing, this typical make up flow event is low flow rate and low volume. The condition described may show up as an intermittent/periodic low flow event below .5 gpm. It may also be captured during a Health Check. Therefore, the call for water at 12 psi may cause a small drip to be detected, however, it is unlikely that the small drip would be alerted on a consistent basis.