Heating System - Bunn Axiom Series Technical Training Manual

The control board monitors the level of water in the tank through a
low voltage level probe (LP2 Probe) mounted to the top of the tank.
When water touches the LP2 probe, the control board grounds a low
voltage AC signal to the tank through minerals in the water and the
inlet solenoid is de-engergized. A relay on the CBA closes it's contacts
to complete the heating circuit and the heating element(s) will now
receive voltage in order to heat the water in the tank. When the CBA
detects water has reached ready temperature with the use of a therm-
istor, the tank will fill to LP1 probe level. The heating circuit will remain
closed until water reaches the set tank temperature.

Heating System

The heating system consists of:
• Water tank
• Heating elements
• Triacs
• Temperature Sensor
• Blanket Warmer
The heating circuit maintains the water in the tank at a preset tempera-
ture; this insures the water is always ready for brewing. Water for brew-
ing is contained in a 200 oz. Stainless steel tank. This tank contains 2
heating elements that are powered by the incoming line voltage to the
machine. Both heating elements are controlled by a relay mounted on
the main control board. The high limit thermostat is located inside the top
cover on the front of the tank, the limit thermostat will interrupt the heat-
ing circuit should the tank overheat.
The control board monitors the water temperature with the use of a
thermistor that is in contact with the water. When water in the tank drops
below the ready temperature, the control board interprets the value of the
thermistor and in return will activate the heater relay to bring the tank
temperature back up to the set tank temperature.
The blanket warmer provides a low consistent heat around the tank at
the point of the temperature sensor. This additional heat aids the heater
circuit by reducing the number of on/off cycles, thereby extending the life
of the relay contacts and the heater.
LP1 Probe
1425 Watt Blanket Heater
LP 2 LP 1
Thermistor
LP2 Probe
2268W
Heating Element
(Dual Volt Models)
1425W
Heating Element
High Limit
Thermostat
Bunn-O-Matic Corporation
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