750-211 (revised 2009)
Promethean Boilers, Model 4WI Manual
3-3
3.2 — Water Requirements
When individual zone circulating pumps are used, it is recommended that they be kept running-even though the
heat users do not require hot water. The relief device or bypass valve will thus allow continuous circulation through
the boiler and can help prevent rapid replacement of boiler water with cold zone water.
3.2.1.4 — Continuous Flow Through the Boiler
The system should be piped and the controls arranged to allow water circulation through the boiler under all oper-
ating conditions. The operation of three-way valves and system controls should be checked to be sure that the
boiler will not be by-passed. Constant circulation through the boiler mitigates the possibility of stratification within
the boiler and results in more even water temperatures to the system.
A rule of thumb of 3/4 to 1 gpm per boiler horsepower can be used to determine the minimum continuous flow
rate through the boiler under all operating conditions. The operator should determine that water flow exists
through the boiler before initial firing or refiring after boiler has been drained.
NOTE: If the operating water temperature going to the system must be lower than 170º F, the operating boiler water
temperature should be a minimum of 170º F (200º F if used to preheat No. 6 oil) and mixing valves should be used to
avoid damage to the equipment.
NOTE: The circulating pumps should be interlocked with the burner so that the burner cannot operate unless the cir-
culating pump is running in order to avoid damage to the equipment.
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