Heater shows E28 and will not start; may be associated with internal safety string.

Safety: Turn off power before testing safety circuits. Never bypass safety devices for normal operation.

• Trace safety string: Using the wiring diagram, identify all safety devices in the series circuit (pressure switch, high limits, rollout switches, etc.).
• Check continuity: With power off, test continuity through each device and the entire string. Replace any device that is open at normal temperature/conditions.
• Inspect wiring: Look for broken wires, loose spade connectors, or corrosion at terminals. Repair or replace as needed.
• Reset manual devices: If any rollout or manual reset limit has tripped, reset once only after determining and correcting the cause.