Crown Boiler BWF Series, Supplement Manual

Page: 13 / 24

11
TABLE 10b .6: EXAMPLES OF THERMAL PURGE OPERATION
Example
#
Call for
Heat
From
Use of
DHW Zone
Thermal Purge Settings Boiler
Temp at
Begin
Call Boiler Behavior Time (
Pt
)
Start Temp
(
St
)
1 T-T N/A 2 min. 140F 130
Heating Circulator starts •
immediately
Burner fires immediately •
2 T-T N/A 2 min. 140F 150
Heating Circulator starts •
immediately
Burner fires when either: •
2 minutes have passed
OR
Temperature falls below 140
3 DHW DHW (dh=
dh
) 2 min. 140F 150
DHW Circulator starts immediately •
Burner fires immediately •
4
Heat T’stat
on DHW
terminals
Heat (dh=
tt2
) 2 min. 140F 150
“DHW” Circulator starts •
immediately
Burner fires when either: •
2 minutes have passed
OR
Temperature falls below 140
5 T-T N/A 2 min. 145F 150
Heating Circulator starts •
immediately
Burner fires when either: •
2 minutes have passed
OR
Temperature falls below 145
6 T-T N/A 3 min. 140 150
Heating Circulator starts immedi- •
ately
Burner fires when either: •
3 minutes have passed
OR
Temperature falls below 140
Pt
(DHW Priority) - If this feature is turned on, and simultaneous calls for heat and DHW are present, the heating circulator will
be forced off for as long as it takes the boiler to satisfy the call for DHW. This feature is sometimes useful when the boiler size is
marginal for the peak DHW demand, but should be used with caution as it can result in lack of heat if the DHW call is very long,
or if there is a problem with the DHW zone which causes the DHW demand to be indefinite. Figure 10b.7 describes the behavior
of both the Heating and DHW Circulators with
Pt
turned both ON and OFF.
dh
(Use of DHW zone) - Although the second zone on the boiler is designated “DHW”, it can be used as a second heating zone by
setting dh = “tt2” instead of dh=”dh”. When the “DHW” zone is used for heating, the thermal purge function is active when this
zone calls for heat. When dh=tt2, the setting of
Pt
(DHW priority) is ignored.
rst
(Reset) - Used to reset the boiler from a hard lockout (as an alternative to momentarily interrupting power to the control).
Pressing the up key will turn rst momentarily to on. When it goes back off (typically within one or two seconds), the control is
reset.