Model LJ Pool and Spa Heater
Page 35
2.
LJ Temperature Control/Ignition Control
Combination System
-
a) Temperature Control-
The Jandy LJ
controller is an electronic control which senses
water temperature by means of a thermistor and
controls heater operation to bring the water to the
temperature selected. It has an option for two
separate thermostat settings which are typically
used to set pool and spa temperatures. A push-
button selector key is used to switch between
settings.
b)
Ignition Control
- The ignition control is
integrated with the temperature control. It
provides energy for ignition of the air/gas mix-
ture, monitors the flame and controls the gas
valve. When the temperature control requires
heat, the ignition control provides a pre-purge of
the combustion chamber. Then it applies electri-
cal power to a hot surface igniter. When the
igniter is hot enough, the ignition control opens
the gas valve. It has sophisticated means to
sense ignition and flame condition so that un-
burned gas will not escape. After the burner is
shut off, the ignition control continues operation
to provide a post-purge period.
3.
Igniter
- The hot surface igniter is a ceramic
composite element which becomes very hot
when electrical power is applied to it. The hot
surface igniter directly ignites the air/gas mixture
in the combustion chamber.
4.
Flame Sensor -
The flame sensor is the elec-
trode through which the ignition control detects
rectification of current passed through the
flame. Inadequate rectification indicates an
unsatisfactory flame condition. The ignition
control responds to the flame signal provided by
the flame sensor.
5.
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.
6.
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 filter is blocked, the pressure switch
prevents operation of the burner. It can be
affected by the installation
7.
Fusible Link
- This is a single-use switch which
detects abnormal temperature in the component
vestibule. It is a fusible link which is held to the
inner panel just above the burner tray by a sheet
metal bracket. Excessive temperature in the
component compartment, possibly due to a
blocked flue or flame roll-out, will cause the link
to fail. This opens the safety circuit which shuts
off the gas valve and shuts the heater down.
FLUE COLLECTOR
HEAT EXCHANGER
COMBUSTION CHAMBER
BURNER
BURNER TRAY SHELF
VENT TOP
EXHAUST
AIR
FLOW
Figure 25. Atmospheric Combustion System
