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Table 3 continued
SYMPTOM
POSSIBLE CAUSE
CHECK
CORRECTIVE ACTION
Motor opens and
will not close (full
heat).
Open circuit in either sensor.
Measure sensor resistance.
Correct sensor wiring or
replace if necessary.
Function switch set to
position 3 (valve
permanently open).
Check function switch setting.
Change function switch
setting to other position,
if necessary.
System "short
cycles"
(repositions
between ON and
OFF at very short
intervals).
Hot water sensor improperly
located.
Check positioning of sensor
relative to heat source.
Relocate sensor.
Ratio setting too high.
Check ratio schedule.
Lower ratio setting by
one position and
monitor system
operation. Reduce ratio
setting by one or more
further positions if
required.
Parallel shift control set too
high; e.g., at +35 F.
Check parallel shift setting and
ratio schedule.
Reduce the parallel shift
setting by 10 F. If system
operation does not
improve, reduce setting
further. Do not alter ratio
setting.
Motor speed preadjustment
incorrectly set to match
motor used in system.
Check motor timing (see tag-on
motor).
Set motor speed
preadjustment to
correspond to speed of
motor used in system
(see page 11).
Valve greatly oversized.
Check rated output against
estimated load requirement.
Reduce system capacity
if necessary.
Differential setting.
Check that setting is not too low.
Adjust as recommended
on page 11.
O PE RATION
■ " .V- ■
GENERAL
Most boiler systems heat water to a constant tempera¬
ture regardless of the outdoor temperature. In fact,
discharge water temperatures in hydronically heated
systems are set sufficiently high to heat a building during
the coldest outdoor temperatures. While this setting is
adequate for extreme settings, it wastes energy during
mild weather by maintaining too much heat in the system
and overheating the building.
Outdoor reset can result in 15% or 20% savings in
heating energy by lowering the boiler discharge water
temperature as the outdoor air temperature increases,
and by programming lower water temperatures during
unoccupied periods. These reset savings are the result of
reduced transmission losses, stack losses, heat losses
from open window control, and use of the timer pro¬
grammer to set back the boiler temperature during
unoccupied periods.
Transmission losses occur when heat is lost through
pipes in non-air conditioned passageways, ceiling and
underground piping routes. Stack losses occur in ail
gas-and oil-fired boilers. Resetting boiler water
discharge temperature downward reduces stack losses. For
optimum savings, return water should be piped around
boilers that are not firing. Open window control losses
occur when occupants attempt to reduce the effects of
overheating by opening windows.
14
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