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for heat has ended.
is will cause the boiler
temperature to rise if no zones are calling for heat. It
is possible to see temperature rise 30º F or more
under a low or no load condition.
place until the boiler's radiation losses match the
heat gain. It is recommended that a dump zone be
connected to dissipate this excess heat to one or
more zones in the system. Se=ing the operating limit
no higher than 180º F allows for the heat rise to
occur without exceeding the recommended
maximum temperatures.
e dump zone control can be used to activate a
zone valve or circulator as a dry contact switch. A
common se=ing for dump zone actuation would be
200º F, with the high limit set point adjusted to 10º F
lower. When this high limit is exceeded, and if
temperature continues to rise until it reaches the
dump zone limit, one or more zones will be
energized and heat distributed until temperatures
fall su:ciently.
If the dump zone is connected to provide heat to
a domestic hot water tank or heat exchanger, a
mixing valve must be installed on the potable
system supply to prevent an unsafe condition of
overheating the domestic hot water.
valve outlet should be set no higher than 125º F for
potable use (for this type of dump zone, see
Appendix H, Example 5).
Non Powered Dump Zone
A non powered dump zone is o;en required to
meet code requirements.
dump boiler heat in the event that power loss
occurs.
is hot-water circulation loop shall be able
to dissipate at least 10% of the estimated rated heat
output of the solid-fuel boiler when circulation is
reduced because of an electrical power failure.
loop can only be made inoperative by a deliberate
manual action.
e design parameters for sizing
shall be a pipe size equal to or greater than 3/4 inch
(18 mm), room temperature of 65ºF (18ºC), and mean
water temperature of 180ºF (82ºC).
e loop shall be positioned above the boiler,
with features that promote natural thermal
circulation of the water.
that excessive pressure will not develop in any
portion of the boiler or system. Larger diameters
is will take
e mixing
is is to provide a way to
e
e piping must be such
may be needed as boiler size increases.
following diagram shows an application example of
how this is accomplished.
Non-Powered Dump Zone
is arrangement will allow a gravity Eow of
heat release in the event of a power failure. For
other dump zone applications.
TESTING/SERVICING ELECTRICAL
COMPONENTS
Note: See Appendix D for a listing of electrical
components. Testing the low water cutoff is
covered earlier in the manual in the section
dedicated to that component.
e electrical components on your SF170/270
boiler are extremely reliable, but any electrical
component can fail. Some testing instructions
follow. Tests are to be conducted by a quali9ed
technician.
High Limit Control
e high limit control functions as a safety in the
event that the operate limit control fails to turn o<
dra; actuation at the proper temperature.
Temperature controls and limits can fail to operate
at the correct temperature, due to wandering from
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e
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