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Page 22
Figure 30. Combustion system diagram.
combustion chamber. Then it applies electrical
power to a "hot surface" igniter. When the igniter
is hot enough, it opens the gas valve. It has
sophisticated means to sense ignition and fl ame
condition so that unburned gas will not escape.
After the burner is shut off, it continues blower
operation to provide a post-purge period.
5.
Igniter - The hot surface igniter is a ceramic
element which becomes very hot when electrical
power is applied to it. It functions both as an
igniter and as fl ame sensor. As a sensor, it is the
electrode through which the ignition control
detects "rectifi cation" of current passed through
the fl ame. Inadequate rectifi cation in di cates an
unsatisfactory fl ame condition. The ignition
control responds to the fl ame signal provided by
the ignitor.
6.
Venturi Pressure Switch - This switch verifi es
that air is fl owing through the combustion system
by sensing pressure reduction at the venturi
throat (relative to pressure at the venturi inlet). It
shuts off the heater if air fl ow is inadequate.
7.
Limit Switches - Two limit switches prevent
excessive water temperature - one within the heat
exchanger and one for water leaving the heater.
If either senses excessive temperature, burner
operation is interrupted.
8.
Water Pressure Switch - This control senses
whether or not water is available to the heater
by measuring back pressure inside of the
heat exchanger. If the pool water pump fails
or the water fi lter is blocked, the pressure
switch pre vents operation of the burner. It can
be affected by the installation conditions as
discussed earlier in this manual.
9.
Burner Temperature Limit Switch - This is a
single-use switch which detects abnormal burner
temperature. It is a disc-type switch which is
held against the burner plenum by a sheet metal
bracket. It has the appearance of an automatic-
reset switch in that it has no reset button.
However, it will reset only if cooled to -31
and therefore will not recycle. The burner limit
switch prevents or interrupts burner operation if
the burner plenum becomes too hot.
10. Vent Limit Switch - The vent limit switch
protects the vent system from excessive exhaust
temperature. It is located on the vent diffuser
above the combustion blower. It interrupts burner
operation if temperature becomes too hot for the
plastic materials used to vent the heater.
See the earlier section entitled Start-up and
Adjustment for the normal sequence of operation.
4D. Combustion Air Filter
The combustion air fi lter is a rectangular foam
fi lter located in a box near the bottom of the control
compartment.. The fi lter removes lint and large scale
dust particles to prevent blockage of the burner media.
The fi lter should be replaced annually in normal
service. Heavy use of the heater or operation in
adverse environments may dictate more frequent
replacement, however. It can be removed through the
bottom of the fi lter box as illustrated in Figure 31.
o
F,
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