ECR International Utica Boilers UB90-50 Installation, Operation & Maintenance Manual page 13

Multi-Zone Systems
Multi-zone systems with two zones are typically piped as
shown in Figures 3 or 4. Multi-zone systems with more than
two zones are likely to have small zones with very low heat
and flow requirements compared to full heating capacity of
the boiler. This can result in very low flow in the boiler if
only one small zone is calling for heat.
Primary Secondary Piping is recommended for multi-zone
systems with more than two zones to insure proper water
flow through the boiler at all times. See Figures 5, 6 and 7
for typical primary secondary piping configurations.
Figure 3 - Two Zone Boiler Piping With Zone Valves
NEAR BOILER PIPING
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SAFETY RELIEF VALVE - SEE PAGE 18
FOR REQUIREMENTS
P/N 240010135 Rev. D [04/15/2017]