Boiler shows E15 and may continue to run at reduced output; indicates communication error with optional modules (e.g., cascade or remote control).

Safety first: Turn off power before working on low-voltage communication wiring.

• Step 1 – Identify communication bus: Locate the terminals or connectors used for remote control, cascade, or BMS communication on the boiler control.
• Step 2 – Check cable connections: Ensure all communication cables are firmly connected at both ends. Look for broken conductors or crushed cable jackets.
• Step 3 – Verify polarity and addressing: Many communication buses require correct polarity (e.g., A/B, +/–) and unique addresses. Compare wiring and dip switch settings to the installation manual.
• Step 4 – Isolate modules: Disconnect external modules one at a time to see if E15 clears. A single faulty module can bring down the bus.
• Step 5 – Replace faulty module or cable: If a specific device or cable segment is identified as the cause, replace it with Bradford White-approved components.

Note: If the boiler operates normally otherwise, E15 may only affect remote monitoring or cascade functions.