Servicing should only be performed by a Qualified Service Agent
47
OPERATION & SERVICE
LWCO - LOW WATER CUT OFF
The water heaters covered in this manual are equipped with a LWCO (low water cut off)
safety device. The control system monitors a LWCO probe (see the images below)
constantly to ensure the water level inside the water heater remains at or above the level
where the probe is installed. The LWCO probe is installed in a threaded fitting in the water
heater’s storage tank. See Figures 1 & 2 on pages 8 & 9 for location. The LWCO probe is
wired to the CCB’s J10 plug - see pages 50 - 52 for location and identification.
LWCO Operation
When the water heater is properly filled with water the end of the LWCO probe is in direct
contact with the water. The CCB emits a low voltage to the LWCO probe and monitors
electrical current flowing through the probe. If the water level in the water heater remains at
or above the level of the probe current will flow from the probe end through the water to the
water heater’s storage tank which is grounded.
If the water level drops below the LWCO probe the control system will declare a LWCO Fault
condition and lock out - see page 79. Voltage to the contactor coils (pages 37 & 38) and
heating elements is terminated to prevent further heating operation.
Inspection and Cleaning
Over time calcium and lime deposits will adhere to the end of the LWCO probe depending
on water hardness, water usage and water temperature. Heavy calcium/lime accumulation
will diminish the current flow through the probe and cause LWCO Fault conditions.
Inspection and cleaning of the LWCO should be performed periodically and any time the
control system declares a LWCO Fault condition.
1 Secure power to the water heater - follow the draining instructions in the maintenance section of the
Instruction Manual that came with the water heater to drain the tank.
2 Disconnect wiring to the LWCO probe and remove it from the water heater.
3 Closely inspect the LWCO for any damage or cracks in the ceramic insulator - replace the LWCO probe if
any cracks or damage is noticed.
4 Clean any calcium/lime deposits from the probe end by gently scraping and using steel wool. Reinstall the
LWCO probe, reconnect wiring to the probe.
5 Follow the filling instructions in the maintenance section of the Instruction Manual that came with the water
heater. Restore power and place the water heater back in service.
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