E03 System sensor failure (cascade)

What the control is telling you

System supply sensor circuit is open or shorted on the cascade master. Display reads SYS SUPPLY SENSOR.

Applies to: EL-80, EL-110, EL-150, EL-220, EL-299, EL-399 (N/LP)

Likely causes

• No system sensor connected to the master boiler
• System sensor faulty
• Short in the sensor wiring (staple through the cable, damaged insulation)
• Open wiring due to defect or damage

Test and repair steps

1. Disconnect the sensor from the wiring and measure its resistance
2. Compare to the resistance table for the temperature; replace the sensor if it does not match
3. If the sensor is good, disconnect both ends of the wiring and check continuity; repair or replace
4. Clears automatically when fixed

Models that show this code

12 models in Elite EL

Other codes on the same units

• E07 Flue temperature high
• E19 Line voltage frequency out of range
• F00 Water high temperature (ECO)
• F01 Flue temperature switch / low water
• F02 Supply sensor failure
• F03 Return sensor failure
• F04 Flue sensor failure
• F05 Supply temperature high