5.2.15 278Error
Error conditions and Check Items
Error Description
E278
System supply temperature sensor open
If an error (open: MΩ) in the system supply temperature sensor is detected, the system displays
the 278E error on the front panel. If this occurs, the boiler initiates shutdown.
Check items
1. Check if the system supply temperature sensor connector is wet due to any reason,
including leakage.
2. Replace the defected system supply temperature sensor.
3. Check circulation pump operating status and for proper flow through the space heating
line.
4. Check the voltage on the PCB to verify proper power to the pump. If there is no voltage,
bleed out air from the system before resetting the unit. If issue persists, replace the pump.
Is the system supply
temperature sensor
normal?
Check connector
(#7 and #8 of CN 13)
Replace system supply thermistor
Resistance between #7 and #8 of CN13
is from 0.437kΩ to 176kΩ at normal
condition. (See page 63-64 for Wiring
Diagram)
No
Yes
Before measuring resistance of the
thermistor, detach the connector
from the PCB.
Check method
Fault Possible Causes Check method
Defective sensor
Defective temperature
sensor connector
Check if the temperature sensor is open and if the connector is connected
properly.
Temperature sensor
Check the resistance of the temperature sensor. (Defective if it is 197kΩ or higher)
●
Replace the temperature sensor if the resistance value is abnormal.
●
Check the temperature displayed on the front panel.
Possible Issues
Defective circulation
pump(external)
Check power supply to the circulation pump(AC 120V)
Defective PCB If the issues continue despite checking the items above, replace the PCB.
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