A112_F: One-Hour Lockout: Water Sense
Status
This is a critical fault experienced by the furnace. The furnace will not operate in gas heat modes but all other modes(e.g. cooling) should function if a call is present. However, if drain is completely blocked in common drain, condensation from the cooling coil in an up-flow configuration with a vent stand pipe above the sensor, water can back up into the secondary heat exchanger and eventually leak internally or get into inducer housing.
Description
The control looks for resistance from pin(s) 1 and/or 2 of connector P4 to chassis ground to determine water sensor flooding in the collector box. When water floods the sensor, the resistance from the sensor terminals to chassis ground decreases significantly. This notifies the control that the collector box is flooded. If this condition persists, the control is locked out for an hour.
Expected Operation
If 4 water sense failures are recorded in a single heat call, alarms "A059_F Water Sensed" and "A112_F One-hour Lockout: Water Sense" will be declared and the control will enter a 1-hour soft lockout. Once lockout time expires and the water sensed condition is no longer present, normal operation will resume. If the heat call is still present, a new heating cycle will be initiated. If water is sensed again within 5 minutes of the new heat cycle, control will be locked out immediately for an hour with alarms "A059_F Water Sensed" and "A112_F One-hour Lockout: Water Sense" declared. This shall repeat until a new heat cycle can progress more than 5 minutes without a water sensed condition or the heat call is no longer present.
Cause
1. A blocked condensate drain or the drain trap has become blocked and cannot allow condensate water to flow properly.
2. Wiring to the sensors has been damaged and exposed wiring is touching the furnace sheet metal.
3. Water sensor has been removed from the collector box with wires still attached and the metal probe is touching the sheet metal portion of the furnace.
4. A blocked drain in the main drain after the furnace and evaporator coil could cause water to back up into the furnace even in cooling mode in an up-flow arrangement. Even though this will not shut the cooling down, water will eventually leak inside the furnace.
Solution
1. Remove/Repair drain blockage.
2. Replace/Repair wiring between control and both sensors.
3. Return sensor(s) to proper location in the collector box.
4. Clear drain all the way to its termination. Make sure furnace condensate piping is correct with vent tee and the vent tee is NOT used to manage evaporator coil condensate.
It is recommended to use separate drains for furnace and evaporator coils. If a common drain is used, vent tee for furnace should be well above any consolidation of drain lines.
