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their original calibration, or fail outright, by not
opening or closing the contained switch at all.
Checking the high limit control would involve
bypassing the operate limit until temperature rises
to the se=ing on the high limit. If the high limit
control fails to open its internal switch, de9ned by
the dra; actuator or force dra; fan continuing to
provide dra;, or by persistence of continuity when
tested a multimeter, it should be replaced.
limit control is installed in one of two 9=ings on the
top of the boiler, near the back.
Operating Limit Control
e operate limit control is normally closed, and
opens on temperature rise. It will either have a 9xed
or adjustable di<erential, to allow for a proper
length of cycle for optimum 9ring.
se=ing will be about 180º F.
9ring once the set temperature has been reach.
When the temperature falls to the number of
degrees below 180º determined by di<erential, the
boiler will resume active 9ring mode. Testing is best
e high
e factory
e boiler will quit
- 14 -
done with a multimeter, testing either for
continuity/lack of continuity under the expected
conditions, or testing for presence or absence of
current across the internal switch. If the control
does not function at the correct temperature, based
on a reference thermometer or the temperature
gauge on the boiler, it should be replaced.
Forced Draft Motor/Draft Actuator
Both the forced dra; fan motor, and the motor
that opens the dra; actuator are self contained,
thermally protected motors.
replaced, and not repaired when they fail to
function. When their function is expected, test for
the presence of current in the leads supplying
power. If power is not being provided, use the
wiring diagram to further troubleshoot why power
is absent from the circuit. If power is present, but
the forced dra; fan motor, or dra; actuator, is not
functioning replace the a<ected component.
ey are typically
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